11 research outputs found
Effet de la libération minérale et des oxy-hydroxydes de fer sur le comportement géochimiques des rejets miniers sulfureux
Lâindustrie miniĂšre, lorsquâelle mĂšne des exploitations de gisements pour produire des minerais devant subir un traitement, est confrontĂ©e Ă diffĂ©rents dĂ©fis et enjeux liĂ©s Ă la gestion des rejets miniers. Le drainage minier acide et la mise en solution des contaminants constituent les principaux problĂšmes environnementaux dus Ă lâexposition des rejets miniers sulfureux Ă lâeau et Ă lâoxygĂšne atmosphĂ©rique. Les rĂ©glementations environnementales obligent les compagnies miniĂšres Ă rĂ©habiliter les sites et en particulier les aires dâentreposage des rejets avant la fermeture de la mine. La gestion des rejets miniers diffĂšre selon le type de lâexploitation et la gĂ©ologie du gisement exploitĂ©. En effet, lors dâune exploitation Ă ciel ouvert, les stĂ©riles miniers sont produits en quantitĂ© considĂ©rables et sont ensuite dĂ©posĂ©s dans des haldes Ă stĂ©riles non-saturĂ©s en eau et caractĂ©risĂ©s par une hĂ©tĂ©rogĂ©nĂ©itĂ© de la distribution granulomĂ©trique. En revanche, lors des exploitations souterraines, moins de stĂ©riles sont gĂ©nĂ©rĂ©s et se sont les rĂ©sidus finement broyĂ©s qui reprĂ©sentent le plus gros des rejets, qui sont dĂ©posĂ©s dans des parcs Ă rĂ©sidus. Dans un climat humide comme celui du Canada, ces derniers sont le plus souvent saturĂ©s en eau avec juste une partie au-dessus de nappe phrĂ©atique en perpĂ©tuel changement de la saturation vers la dĂ©saturation. Dans les deux cas (stĂ©riles et rĂ©sidus), la prĂ©diction du comportement gĂ©ochimique des rejets miniers est un paramĂštre important qui influence grandement la faisabilitĂ© dâun projet minier. Durant ce doctorat, les deux types de rejets miniers ont Ă©tĂ© Ă©tudiĂ©s au vu de deux objectifs diffĂ©rents sachant la diffĂ©rence de leurs propriĂ©tĂ©s mais cependant pour la mĂȘme finalitĂ© qui est de mieux prĂ©dire et gĂ©rer le rejet minier en question. Pour ce qui est des stĂ©riles, une nouvelle mĂ©thode de gestion est proposĂ©e en amont lors de leur extraction et avant leur entreposage. Quant aux rĂ©sidus Ă©tudiĂ©s, des formulations dâamendements alcalins et cimentaires ont Ă©tĂ© testĂ©es en cellules de terrain comme technique de stabilisation/solidification des rĂ©sidus miniers oxydĂ©s gĂ©nĂ©rateurs dâacide aprĂšs avoir dĂ©montrĂ© lâeffet des oxy-hydroxydes de fer sur le comportement gĂ©ochimique des rĂ©sidus miniers.
Trois lithologies de stĂ©riles ont Ă©tĂ© Ă©chantillonnĂ©es Ă la mine Canadian Malartic juste aprĂšs dynamitage pour respecter la reprĂ©sentativitĂ© du paramĂštre âdistribution granulomĂ©triqueâ; souvent mal considĂ©rĂ© par les Ă©tudes de nos jours. Les trois lithologies CPO (lithologie A), AGR (lithologie B) et CGR (lithologie C) ont Ă©tĂ© sĂ©parĂ©es en sept fractions granulomĂ©triques (-53ÎŒm, +53ÎŒm/-300ÎŒm, +300ÎŒm/-850ÎŒm, +850ÎŒm/-2.4mm, +2.4mm/-5mm, +5mm/-1.5cm, +1.5cm/-5cm). La caractĂ©risation chimique et minĂ©ralogique a montrĂ© que les trois lithologies et leurs fractions
contiennent plus de carbonates (â„2.5%) par rapport aux sulfures (â€1.5%). Les carbonates sont majoritairement reprĂ©sentĂ©s par la calcite et les sulfures sont principalement constituĂ©s de pyrite. Le contenu en sulfures varie en fonction de la fraction granulomĂ©trique. En effet, les fractions fines sont plus enrichies en sulfures par rapport aux fractions grossiĂšres. En terme textural, lâanalyse minĂ©ralogique a montrĂ© que les sulfures sont libres au niveau des fractions fines (95%) et inclus au niveau des fractions grossiĂšres et idem pour les carbonates. Par ailleurs, le degrĂ© de libĂ©ration de sulfures devient presque nĂ©gligeable (5%) Ă partir de 2.4 mm comme diamĂštre des grains pour les trois lithologies par comparaison au degrĂ© de libĂ©ration des carbonates qui reste non-nĂ©gligeable (10%) Ă 2.4mm offrant une sĂ©curitĂ©. En consĂ©quence, 2.4mm a Ă©tĂ© dĂ©fini comme le diamĂštre limite dâencapsulation physique de sulfures (DPLS) pour ces trois Ă©chantillons. Le DPLS est dĂ©fini comme un seuil qui sĂ©pare un stĂ©rile minier en deux fractions granulomĂ©triques dĂ©pendamment de leurs rĂ©activitĂ©s : i) la fraction fine (-DPLS) qui constitue ĂȘtre la fraction rĂ©active et probablement problĂ©matique et ii) la fraction grossiĂšre (+DPLS) qui constitue ĂȘtre la fraction non rĂ©active et ne prĂ©senterait pas un risque liĂ© Ă lâoxydation des sulfures. La fraction -DPLS reprĂ©sente une proportion faible de lâĂ©chantillon total (moins de 23% considĂ©rant 1m comme Dmax pour la lithologie A) par rapport Ă la fraction +DPLS qui reprĂ©sente la majoritĂ© de lâĂ©chantillon total. En plus de la caractĂ©risation chimico-minĂ©ralogique et les tests statiques, des essais cinĂ©tiques en colonnes ont Ă©tĂ© monitorĂ©s sur une pĂ©riode 543 jours pour confirmer cette conclusion. Les trois lithologies ont Ă©tĂ© sĂ©parĂ©es en deux fractions granulomĂ©triques Ă savoir -2.4mm et +2.4mm tout en testant lâĂ©chantillon total aussi. Les rĂ©sultats du suivi gĂ©ochimique ont montrĂ© quâeffectivement la fraction -2.4mm est beaucoup plus rĂ©active que la fraction +2.4mm et lâĂ©chantillon total. La lithologie B Ă©tait la lithologie la plus rĂ©active; le taux dâoxydation de la pyrite au niveau de sa fraction -2.4mm Ă©tait de 12.5 ÎŒmol/kg/jour, au niveau de sa fraction +2.4mm Ă©tait de lâordre de 0.27 ÎŒmol/kg/jour et le taux dâoxydation au niveau de lâĂ©chantillon total Ă©tait de lâordre 2.45 ÎŒmol/kg/jour. La mĂȘme tendance a Ă©tĂ© remarquĂ©e pour les deux autres lithologies. LâintĂ©rĂȘt du calcul du DPLS se situe au niveau des Ă©ventuels gains Ă©conomiques qui peuvent avoir lieu sâil est intĂ©grĂ© en amont de la gestion des stĂ©riles miniers. En effet, au lieu de gĂ©rer les stĂ©riles comme une seule entitĂ©, il est maintenant suggĂ©rĂ© de les sĂ©parer en deux fractions; une fraction rĂ©active (-DPLS) et une fraction non rĂ©active (+DPLS) sachant que la fraction rĂ©active prĂ©sente une faible proportion de lâĂ©chantillon total et quâelle puisse ĂȘtre soit dĂ©posĂ© avec les rĂ©sidus minier soit encore traitĂ©s mĂ©tallurgiquement et Ă©conomiquement elle devenait intĂ©ressante.
Par ailleurs, la problĂ©matique de prĂ©diction du comportement gĂ©ochimique des rĂ©sidus miniers est diffĂ©rente de celle liĂ©e aux stĂ©riles miniers. Les rĂ©sidus miniers, par comparaison aux stĂ©riles miniers, sont caractĂ©risĂ©s par une granulomĂ©trie fine; ce qui favorise et accĂ©lĂšre mĂȘme les taux de rĂ©actions dans des conditions non saturĂ©es (oxydation des sulfures, dissolution des carbonates). Le comportement gĂ©ochimique des rĂ©sidus miniers est gĂ©nĂ©ralement Ă©valuĂ© en utilisant des essais cinĂ©tiques au laboratoire. Ces essais sont conçus pour simuler lâoxydation naturelle des rĂ©sidus miniers et ont dĂ©montrĂ© leurs capacitĂ©s Ă prĂ©dire adĂ©quatement le comportement gĂ©ochimique des rejets miniers. Cependant, le cas des rĂ©sidus miniers de Joutel tĂ©moigne de lâimportance de considĂ©rer la composante du terrain pour bien comprendre le comportement gĂ©ochimique des rĂ©sidus miniers. Le parc Ă rĂ©sidus de Joutel qui sâĂ©tend sur une superficie de 120 ha est fermĂ© depuis environ 25 ans. Lâexposition des rĂ©sidus aux agents atmosphĂ©riques a causĂ© lâapparition dâun horizon oxydĂ© Ă la surface du parc Ă rĂ©sidus avec une formation localisĂ©e du hardpan tendant Ă se gĂ©nĂ©raliser sur tout le site. Ce dernier est dĂ©fini comme une couche cimentaire qui se forme Ă lâinterface entre lâhorizon oxydĂ© et lâhorizon des rĂ©sidus frais par prĂ©cipitation des oxy-hydroxydes de fer. La caractĂ©risation minĂ©ralogique et chimique a montrĂ© un Ă©puisement des sulfures et des carbonates en allant du rĂ©sidu frais vers le rĂ©sidu oxydĂ© avec un changement de texture assez remarquable au niveau du hardpan. Les essais cinĂ©tiques rĂ©alisĂ©s sur les rĂ©sidus frais ont montrĂ© quâil sâagit dâun comportement non-gĂ©nĂ©rateur dâacide Ă long terme. Cependant, sur le parc Ă rĂ©sidus de Joutel, une aciditĂ© a Ă©tĂ© gĂ©nĂ©rĂ©e Ă travers de la couche oxydĂ©e. Ce constat a Ă©tĂ© confirmĂ© moyennant des essais cinĂ©tiques sur des rĂ©sidus oxydĂ©s. Ătant donnĂ© que le rĂ©sidu oxydĂ© est le rĂ©sultat de lâoxydation du rĂ©sidu frais sur environ 25 ans et que la prĂ©diction du comportement gĂ©ochimique du rĂ©sidu frais Ă©tait non-gĂ©nĂ©rateur dâacide mais le rĂ©sidu oxydĂ© a montrĂ© un comportement acidogĂšne, ceci prouve lâincapacitĂ© des essais cinĂ©tiques Ă prĂ©dire correctement le comportement gĂ©ochimique des rĂ©sidus miniers de Joutel. AprĂšs une investigation sur le terrain et au laboratoire, le rĂŽle essentiel du hardpan sur le comportement gĂ©ochimique global des rĂ©sidus miniers de Joutel est dĂ©montrĂ©. En effet, lâoccurrence du hardpan constitue un Ă©cran aux les Ă©coulements verticaux des eaux. La formation du hardpan, caractĂ©risĂ© par sa faible permĂ©abilitĂ© estimĂ©e par analyse tomographique, favorise les Ă©coulements latĂ©raux (ruissellement de surface) au dĂ©pend des Ă©coulements verticaux des eaux de surface. Câest pour cette raison que la gĂ©ochimie globale du parc Ă rĂ©sidus de Joutel est influencĂ©e grandement par la rĂ©activitĂ© des rĂ©sidus oxydĂ©s en surface. Ces derniers sont caractĂ©risĂ©s par un Ă©puisement plus ou moins important des sulfures, constat confirmĂ© par les essais de consommation dâoxygĂšne. Dans les zones oxydĂ©es, les flux dâoxygĂšne ne dĂ©passent pas 30 mole/m2/annĂ©e. En plus de leurs rĂ©activitĂ©s faibles, les rĂ©sidus oxydĂ©s sont caractĂ©risĂ©s par lâabondance des minĂ©raux secondaires Ă lâexemple du gypse et des oxy-hydroxydes de fer. Ces oxy-hydroxydes de fer, qui Ă©taient responsables de lâattĂ©nuation des rĂ©ponses gĂ©ochimiques de lâoxydation des rĂ©sidus frais, peuvent rĂ©agir diffĂ©remment en gĂ©nĂ©rant de lâaciditĂ©. La rĂ©partition spatiale de lâaciditĂ© au niveau du parc Ă rĂ©sidus de Joutel nâĂ©tait pas systĂ©matique. En effet, lâĂ©chantillonnage systĂ©matique rĂ©alisĂ© Ă Joutel a permis de cartographier la variabilitĂ© spatiale des propriĂ©tĂ©s gĂ©ochimiques des rĂ©sidus oxydĂ©s. Lâutilisation des SIG a permis de dĂ©limiter les zones les plus problĂ©matiques et qui Ă©taient localisĂ©es Ă lâouest du parc Sud et au nord du parc Nord, ce qui a permis de proposer un schĂ©ma conceptuel illustrant le comportement des rĂ©sidus Ă Joutel. Par la suite, les amendements alcalins et cimentaires ont Ă©tĂ© proposĂ©s et testĂ©s comme technique de stabilisation/solidification sur le site Joutel. Lâutilisation du calcaire Ă 5 et 10 wt.% a permis une neutralisation immĂ©diate du pH des lixiviats et la plupart des Ă©lĂ©ments chimiques ont Ă©tĂ© immobilisĂ©s grĂące Ă la prĂ©cipitation des phases secondaires dans des conditions proches de la neutralitĂ©. Cependant, les concentrations en Zn et en As Ă©taient parfois plus grandes dans les lixiviats provenant des rĂ©sidus amendĂ©s par rapport Ă la cellule tĂ©moin. Les amendements cimentaires ont Ă©tĂ© testĂ©s en utilisant le ciment portland et les cendres volantes de la combustion de la biomasse produites en rĂ©gion Ă un dosage total de 5%. La premiĂšre formulation qui contenait 50% ciment et 50% cendres volantes a montrĂ© des rĂ©sultats prometteurs concernant la stabilisation des contaminants. LâefficacitĂ© de ces amendements Ă court terme a Ă©tĂ© dĂ©montrĂ©, mais il reste Ă Ă©tudier leurs efficacitĂ©s Ă long terme ainsi que les coĂ»ts Ă©conomiques liĂ©s Ă cette alternative
Effet de la libération minérale et des oxy-hydroxydes de fer sur le comportement géochimique des rejets miniers sulfureux
Lâindustrie miniĂšre, lorsquâelle mĂšne des exploitations de gisements pour produire des minerais devant subir un traitement, est confrontĂ©e Ă diffĂ©rents dĂ©fis et enjeux liĂ©s Ă la gestion des rejets miniers. Le drainage minier acide et la mise en solution des contaminants constituent les principaux problĂšmes environnementaux dus Ă lâexposition des rejets miniers sulfureux Ă lâeau et Ă lâoxygĂšne atmosphĂ©rique. Les rĂ©glementations environnementales obligent les compagnies miniĂšres Ă rĂ©habiliter les sites et en particulier les aires dâentreposage des rejets avant la fermeture de la mine. La gestion des rejets miniers diffĂšre selon le type de lâexploitation et la gĂ©ologie du gisement exploitĂ©. En effet, lors dâune exploitation Ă ciel ouvert, les stĂ©riles miniers sont produits en quantitĂ© considĂ©rables et sont ensuite dĂ©posĂ©s dans des haldes Ă stĂ©riles non-saturĂ©s en eau et caractĂ©risĂ©s par une hĂ©tĂ©rogĂ©nĂ©itĂ© de la distribution granulomĂ©trique. En revanche, lors des exploitations souterraines, moins de stĂ©riles sont gĂ©nĂ©rĂ©s et se sont les rĂ©sidus finement broyĂ©s qui reprĂ©sentent le plus gros des rejets, qui sont dĂ©posĂ©s dans des parcs Ă rĂ©sidus. Dans un climat humide comme celui du Canada, ces derniers sont le plus souvent saturĂ©s en eau avec juste une partie au-dessus de nappe phrĂ©atique en perpĂ©tuel changement de la saturation vers la dĂ©saturation. Dans les deux cas (stĂ©riles et rĂ©sidus), la prĂ©diction du comportement gĂ©ochimique des rejets miniers est un paramĂštre important qui influence grandement la faisabilitĂ© dâun projet minier. Durant ce doctorat, les deux types de rejets miniers ont Ă©tĂ© Ă©tudiĂ©s au vu de deux objectifs diffĂ©rents sachant la diffĂ©rence de leurs propriĂ©tĂ©s mais cependant pour la mĂȘme finalitĂ© qui est de mieux prĂ©dire et gĂ©rer le rejet minier en question. Pour ce qui est des stĂ©riles, une nouvelle mĂ©thode de gestion est proposĂ©e en amont lors de leur extraction et avant leur entreposage. Quant aux rĂ©sidus Ă©tudiĂ©s, des formulations dâamendements alcalins et cimentaires ont Ă©tĂ© testĂ©es en cellules de terrain comme technique de stabilisation/solidification des rĂ©sidus miniers oxydĂ©s gĂ©nĂ©rateurs dâacide aprĂšs avoir dĂ©montrĂ© lâeffet des oxy-hydroxydes de fer sur le comportement gĂ©ochimique des rĂ©sidus miniers. Trois lithologies de stĂ©riles ont Ă©tĂ© Ă©chantillonnĂ©es Ă la mine Canadian Malartic juste aprĂšs dynamitage pour respecter la reprĂ©sentativitĂ© du paramĂštre âdistribution granulomĂ©triqueâ; souvent mal considĂ©rĂ© par les Ă©tudes de nos jours. Les trois lithologies CPO (lithologie A), AGR (lithologie B et CGR (lithologie C) ont Ă©tĂ© sĂ©parĂ©es en sept fractions granulomĂ©triques (-53”m, +53”m/-300”m, +300”m/-850”m, +850”m/-2.4mm, +2.4mm/-5mm, +5mm/-1.5cm, +1.5cm/-5cm). La caractĂ©risation chimique et minĂ©ralogique a montrĂ© que les trois lithologies et leurs fractions contiennent plus de carbonates (â„2.5%) par rapport aux sulfures (â€1.5%). Les carbonates sont majoritairement reprĂ©sentĂ©s par la calcite et les sulfures sont principalement constituĂ©s de pyrite. Le contenu en sulfures varie en fonction de la fraction granulomĂ©trique. En effet, les fractions fines sont plus enrichies en sulfures par rapport aux fractions grossiĂšres. En terme textural, lâanalyse minĂ©ralogique a montrĂ© que les sulfures sont libres au niveau des fractions fines (95%) et inclus au niveau des fractions grossiĂšres et idem pour les carbonates. Par ailleurs, le degrĂ© de libĂ©ration de sulfures devient presque nĂ©gligeable (5%) Ă partir de 2.4 mm comme diamĂštre des grains pour les trois lithologies par comparaison au degrĂ© de libĂ©ration des carbonates qui reste non-nĂ©gligeable (10%) Ă 2.4mm offrant une sĂ©curitĂ©. En consĂ©quence, 2.4mm a Ă©tĂ© dĂ©fini comme le diamĂštre limite dâencapsulation physique de sulfures (DPLS) pour ces trois Ă©chantillons. Le DPLS est dĂ©fini comme un seuil qui sĂ©pare un stĂ©rile minier en deux fractions granulomĂ©triques dĂ©pendamment de leurs rĂ©activitĂ©s : i) la fraction fine (-DPLS) qui constitue ĂȘtre la fraction rĂ©active et probablement problĂ©matique et ii) la fraction grossiĂšre (+DPLS) qui constitue ĂȘtre la fraction non rĂ©active et ne prĂ©senterait pas un risque liĂ© Ă lâoxydation des sulfures. La fraction -DPLS reprĂ©sente une proportion faible de lâĂ©chantillon total (moins de 23% considĂ©rant 1m comme Dmax pour la lithologie A) par rapport Ă la fraction +DPLS qui reprĂ©sente la majoritĂ© de lâĂ©chantillon total. En plus de la caractĂ©risation chimico-minĂ©ralogique et les tests statiques, des essais cinĂ©tiques en colonnes ont Ă©tĂ© monitorĂ©s sur une pĂ©riode 543 jours pour confirmer cette conclusion. Les trois lithologies ont Ă©tĂ© sĂ©parĂ©es en deux fractions granulomĂ©triques Ă savoir -2.4mm et +2.4mm tout en testant lâĂ©chantillon total aussi. Les rĂ©sultats du suivi gĂ©ochimique ont montrĂ© quâeffectivement la fraction -2.4mm est beaucoup plus rĂ©active que la fraction +2.4mm et lâĂ©chantillon total. La lithologie B Ă©tait la lithologie la plus rĂ©active; le taux dâoxydation de la pyrite au niveau de sa fraction -2.4mm Ă©tait de 12.5 ”mol/kg/jour, au niveau de sa fraction +2.4mm Ă©tait de lâordre de 0.27 ”mol/kg/jour et le taux dâoxydation au niveau de lâĂ©chantillon total Ă©tait de lâordre 2.45 ”mol/kg/jour. La mĂȘme tendance a Ă©tĂ© remarquĂ©e pour les deux autres lithologies. LâintĂ©rĂȘt du calcul du DPLS se situe au niveau des Ă©ventuels gains Ă©conomiques qui peuvent avoir lieu sâil est intĂ©grĂ© en amont de la gestion des stĂ©riles miniers. En effet, au lieu de gĂ©rer les stĂ©riles comme une seule entitĂ©, il est maintenant suggĂ©rĂ© de les sĂ©parer en deux fractions; une fraction rĂ©active (-DPLS) et une fraction non rĂ©active (+DPLS) sachant que la fraction rĂ©active prĂ©sente une faible proportion de lâĂ©chantillon total et quâelle puisse ĂȘtre soit dĂ©posĂ© avec les rĂ©sidus minier soit encore traitĂ©s mĂ©tallurgiquement et Ă©conomiquement elle devenait intĂ©ressante. Par ailleurs, la problĂ©matique de prĂ©diction du comportement gĂ©ochimique des rĂ©sidus miniers est diffĂ©rente de celle liĂ©e aux stĂ©riles miniers. Les rĂ©sidus miniers, par comparaison aux stĂ©riles miniers, sont caractĂ©risĂ©s par une granulomĂ©trie fine; ce qui favorise et accĂ©lĂšre mĂȘme les taux de rĂ©actions dans des conditions non saturĂ©es (oxydation des sulfures, dissolution des carbonates). Le comportement gĂ©ochimique des rĂ©sidus miniers est gĂ©nĂ©ralement Ă©valuĂ© en utilisant des essais cinĂ©tiques au laboratoire. Ces essais sont conçus pour simuler lâoxydation naturelle des rĂ©sidus miniers et ont dĂ©montrĂ© leurs capacitĂ©s Ă prĂ©dire adĂ©quatement le comportement gĂ©ochimique des rejets miniers. Cependant, le cas des rĂ©sidus miniers de Joutel tĂ©moigne de lâimportance de considĂ©rer la composante du terrain pour bien comprendre le comportement gĂ©ochimique des rĂ©sidus miniers. Le parc Ă rĂ©sidus de Joutel qui sâĂ©tend sur une superficie de 120 ha est fermĂ© depuis environ 25 ans. Lâexposition des rĂ©sidus aux agents atmosphĂ©riques a causĂ© lâapparition dâun horizon oxydĂ© Ă la surface du parc Ă rĂ©sidus avec une formation localisĂ©e du hardpan tendant Ă se gĂ©nĂ©raliser sur tout le site. Ce dernier est dĂ©fini comme une couche cimentaire qui se forme Ă lâinterface entre lâhorizon oxydĂ© et lâhorizon des rĂ©sidus frais par prĂ©cipitation des oxy-hydroxydes de fer. La caractĂ©risation minĂ©ralogique et chimique a montrĂ© un Ă©puisement des sulfures et des carbonates en allant du rĂ©sidu frais vers le rĂ©sidu oxydĂ© avec un changement de texture assez remarquable au niveau du hardpan. Les essais cinĂ©tiques rĂ©alisĂ©s sur les rĂ©sidus frais ont montrĂ© quâil sâagit dâun comportement non-gĂ©nĂ©rateur dâacide Ă long terme. Cependant, sur le parc Ă rĂ©sidus de Joutel, une aciditĂ© a Ă©tĂ© gĂ©nĂ©rĂ©e Ă travers de la couche oxydĂ©e. Ce constat a Ă©tĂ© confirmĂ© moyennant des essais cinĂ©tiques sur des rĂ©sidus oxydĂ©s. Ătant donnĂ© que le rĂ©sidu oxydĂ© est le rĂ©sultat de lâoxydation du rĂ©sidu frais sur environ 25 ans et que la prĂ©diction du comportement gĂ©ochimique du rĂ©sidu frais Ă©tait non-gĂ©nĂ©rateur dâacide mais le rĂ©sidu oxydĂ© a montrĂ© un comportement acidogĂšne, ceci prouve lâincapacitĂ© des essais cinĂ©tiques Ă prĂ©dire correctement le comportement gĂ©ochimique des rĂ©sidus miniers de Joutel. AprĂšs une investigation sur le terrain et au laboratoire, le rĂŽle essentiel du hardpan sur le comportement gĂ©ochimique global des rĂ©sidus miniers de Joutel est dĂ©montrĂ©. En effet, lâoccurrence du hardpan constitue un Ă©cran aux les Ă©coulements verticaux des eaux. La formation du hardpan, caractĂ©risĂ© par sa faible permĂ©abilitĂ© estimĂ©e par analyse tomographique, favorise les Ă©coulements latĂ©raux (ruissellement de surface) au dĂ©pend des Ă©coulements verticaux des eaux de surface. Câest pour cette raison que la gĂ©ochimie globale du parc Ă rĂ©sidus de Joutel est influencĂ©e grandement par la rĂ©activitĂ© des rĂ©sidus oxydĂ©s en surface. Ces derniers sont caractĂ©risĂ©s par un Ă©puisement plus ou moins important des sulfures,constat confirmĂ© par les essais de consommation dâoxygĂšne. Dans les zones oxydĂ©es, les flux dâoxygĂšne ne dĂ©passent pas 30 mole/m2/annĂ©e. En plus de leurs rĂ©activitĂ©s faibles, les rĂ©sidus oxydĂ©s sont caractĂ©risĂ©s par lâabondance des minĂ©raux secondaires Ă lâexemple du gypse et des oxy-hydroxydes de fer. Ces oxy-hydroxydes de fer, qui Ă©taient responsables de lâattĂ©nuation des rĂ©ponses gĂ©ochimiques de lâoxydation des rĂ©sidus frais, peuvent rĂ©agir diffĂ©remment en gĂ©nĂ©rant de lâaciditĂ©. La rĂ©partition spatiale de lâaciditĂ© au niveau du parc Ă rĂ©sidus de Joutel nâĂ©tait pas systĂ©matique. En effet, lâĂ©chantillonnage systĂ©matique rĂ©alisĂ© Ă Joutel a permis de cartographier la variabilitĂ© spatiale des propriĂ©tĂ©s gĂ©ochimiques des rĂ©sidus oxydĂ©s. Lâutilisation des SIG a permis de dĂ©limiter les zones les plus problĂ©matiques et qui Ă©taient localisĂ©es Ă lâouest du parc Sud et au nord du parc Nord, ce qui a permis de proposer un schĂ©ma conceptuel illustrant le comportement des rĂ©sidus Ă Joutel. Par la suite, les amendements alcalins et cimentaires ont Ă©tĂ© proposĂ©s et testĂ©s comme technique de stabilisation/solidification sur le site Joutel. Lâutilisation du calcaire Ă 5 et 10 wt.% a permis une neutralisation immĂ©diate du pH des lixiviats et la plupart des Ă©lĂ©ments chimiques ont Ă©tĂ© immobilisĂ©s grĂące Ă la prĂ©cipitation des phases secondaires dans des conditions proches de la neutralitĂ©. Cependant, les concentrations en Zn et en As Ă©taient parfois plus grandes dans les lixiviats provenant des rĂ©sidus amendĂ©s par rapport Ă la cellule tĂ©moin. Les amendements cimentaires ont Ă©tĂ© testĂ©s en utilisant le ciment portland et les cendres volantes de la combustion de la biomasse produites en rĂ©gion Ă un dosage total de 5%. La premiĂšre formulation qui contenait 50% ciment et 50% cendres volantes a montrĂ© des rĂ©sultats prometteurs concernant la stabilisation des contaminants. LâefficacitĂ© de ces amendements Ă court terme a Ă©tĂ© dĂ©montrĂ©, mais il reste Ă Ă©tudier leurs efficacitĂ©s Ă long terme ainsi que les coĂ»ts Ă©conomiques liĂ©s Ă cette alternative. Mots clĂ©s : rejets miniers, le degrĂ© de libĂ©ration minĂ©rale, sĂ©paration des stĂ©riles, hardpan, minĂ©raux secondaires, amendements miniers.
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Abstract
During ore extraction and processing, mining industries generate high quantities of solid mine wastes. Their management during all mine life cycle is a serious challenge facing these industries. Acid mine drainage and contaminants mobilization constitute the most known problems related to exposition of sulphidic mine wastes to atmospheric oxygen and water. Conformity to current environmental regulations and standards requires mine sites reclamation and especially waste storage facilities before the final closure of mine sites. Mine waste management depends on the extraction method and the geological properties of the deposit. Hereafter, mine waste will refer to waste produced mostly during open pits extraction (compared to underground exploitation) and which didnât go through ore processing steps, mine tailings refer to finely grinded tailings and produced during ore processing. Waste rocks are mostly deposited in large surface unsaturated waste rock piles, and mine tailings are deposited in slurry state in tailings storage facilities. In Canada, the environmental behavior of waste rocks and tailings is one of the parameter which is considered during mine project feasibility studies. This is why, prediction of environmental behavior of waste rocks and mine tailings becomes a serious concern of mining industries all around the world. During this study, waste rocks and tailings were studied in order to improve understanding of geochemical reactions within waste rocks and mine tailings which will be used for a better prediction of their environmental behavior. Concerning waste rocks, a novel methodology was suggested to consider mineral textures (mineral liberation and mineralogical associations) during characterization steps. As demonstrated in this study, a new method of waste management is suggested, and it consisted on waste rock sorting considering the diameter of physical locking of sulphides. Concerning mine tailings, it is demonstrated in this study that iron-oxyhydroxides is very common phenomenon occurring during sulfides oxidation and carbonates dissolution and it could influence the prediction of the geochemical behavior of mine tailings which may require in some cases to consider the field conditions. Finally, four amendment formulations (cementitious and alkaline) were tested in the field conditions and showed promising results to stabilize/solidify oxidized acid generating tailings. Three waste rock (WR) lithologies was collected from Canadian Malartic mine immediately after in-situ WR blasting to consider the actual particle distribution which is rarely considered during nowadays studies. The three lithologies CPO (lithology A), AGR (lithology B) and CGR (lithology C were divided into seven fractions (-53”m, +53”m/-300”m, +300”m/-850”m, +850”m/-2.4mm,+2.4mm/-5mm, +5mm/-1.5cm, +1.5cm/-5cm). the chemical and mineralogical characterization showed that the three total samples and their fractions contained more carbonates mainly as calcite (â„2.5%) than sulphides mostly as pyrite (â€1.5%). Sulphides content depended on the particle size, fine particle sizes were more enriched in sulphides compared to coarse fractions. Moreover, automated mineralogy characterization performed on the concerned fractions showed that sulphides are mostly liberated (95%) within fine fractions compared to coarser fractions where sulphides are mostly encapsulated within non-sulphide gangue (NSG) and their liberation is almost negligible (5%). Based on mineral textures analysis within the studied lithologies, 2.4mm was defined as the diameter of physical locking of sulphides (DPLS). The DPLS defines a critical particle size that could be used to divide a waste rock into two fractions with extremely different reactivities: the fraction -DPLS is the most reactive one and it consists on only a low proportion of total samples (â€23 %) and the fraction +DPLS which is characterized by a low sulphide oxidation. This diameter was also confirmed using kinetic tests monitored for 543 days. The three lithologies were divided into two fractions which are the sample -2.4mm and +2.4mm and the total sample was tested separately. Results of geochemical monitoring showed that the fraction -2.4mm of the three lithologies was the most reactive fraction compared to total sample and the fraction +2.4mm. The lithology B was the most reactive one, pyrite oxidation rates of fraction -2.4mm, total sample and fraction +2.4mm were about 12.5 ”mol/kg/day, 2.45 ”mol/kg/day and 0.27 ”mol/kg/day respectively. Tendency of pyrite oxidation rates between the different fractions of the lithology B was the same for the two other lithologies A and C. Calculation and determination of DPLS will allow to challenge waste management. Indeed, the use of this parameter will allow depositing waste rocks into two waste rock piles instead of one. A pile which will contain only particles -DPLS and another one containing particles +DPLS. Consequently, the volume of the reactive part of the waste rocks will be minimized considerably and so economic cost related to waste rocks management.Otherwise, the challenge related to prediction of the geochemical behavior of mine tailings is different to that related to waste rocks. Mine tailings, compared to waste rocks, are characterized by fine and homogeneous particle size distribution; which accelerates reactions rates in unsaturated conditions (sulphides oxidation and carbonates dissolution). The geochemical behavior of mine tailings is usually studied using laboratory kinetic testing. This kinetic testing is deigned to simulate the natural oxidation of tailings. However, Joutelâs tailings are an example of the importance of considering the field conditions to understand correctly the actual geochemical behavior of mine tailings. Joutel is a closed tailing storage facility (TSF) of about 120 ha for 25 years. Tailings exposition to water and oxygen lead to apparition of an oxidized horizon and local formation of hardpans which may be a generalized phenomenon in the TSF. The hardpan is defined as cementitious layers that occur at the interface between the oxidized horizon and the unweathered tailings due to iron oxy-hydroxides precipitation. The chemical and mineralogical characterization showed that carbonates and sulphides depletion increases from the unweathered tailings to the oxidized horizon with a spectacular change regarding the minerals texture. Knowing that the oxidized horizon is the result of oxidation of the unweathered tailings for 25 years and the geochemical behavior of the unweathered tailings was predicted as non-acid generating, however the oxidized tailings were acidic in some location in the TSF; this shows the incapacity of kinetic testing in this case to predict correctly the geochemical behavior of Joutelâs unweathered tailings. Laboratory and field investigations showed the effect of hardpans on the geochemical behavior of Joutelâs TSF. Indeed, hardpan constitutes a screen against vertical water flows due its low porosity as analyzed using computed tomography. Consequently, hardpans occurrence deflects water vertical infiltration and enhances surface and sub-surface runoff. This why the reactivity of the TSF is almost controlled by the reactivity of upper oxidized tailings. These oxidized tailings are characterized by high sulphides depletion as demonstrated using oxygen consumption tests. Oxygen consumption within oxidized tailings didnât exceed 30 mole/m2/year. Furthermore, oxidized tailings are mainly formed by secondary minerals such as gypsum and iron oxy-hydroxides. These iron oxy-hydroxides which were responsible for metals/metalloids attenuation may react again and release the sorbed elements and generate acidity. The spatial mapping of the acidity and the geochemical properties of Joutelâs TSF showed that they were spatially dependent. The use of GIS allowed delimiting the zones of acidity which were spatially located at the west of the south zone and at the north of the north zone. Consequently, a conceptual model was proposed to explain the geochemistry of Joutelâs tailings. Then, alkaline and cementitious amendments were tested as mitigation scenario to stabilize oxidized tailings. Thus, the use of 5% and 10% limestone allowed an immediate pH buffering and immobilization of the most chemical species. The chemical species were stabilized within limestone dissolution by iron-oxyhydroxides precipitation at neutral conditions. However, zinc and arsenic were sometimes more released within the amended tailings. The cementitious amendments were tested using ordinary cement and fly ash with 5% dosage. The first formulation consisted on 50:50 cement and fly ash showed promising results concerning the chemical species stabilization. The efficiency and the cost of these amendments must be studied at the long-term scale. Key words: Tailings, waste rocks, mineral liberation degree, waste rock sorting, hardpan, secondary minerals, mining amendments
Evaluation of the Anthropogenic Metal Pollution at Osisko Lake: Sediments Characterization for Reclamation Purposes
The anthropogenic pollution of lake ecosystems by human activities (e.g., mining industries) is recognized as a serious issue. The Osisko urban lake located in Rouyn-Noranda (Quebec, Canada) was used partially as a waste disposal facility for many decades, causing a heavy pollution. The main undertakings of this study are (i) assessing the mineralogical and geochemical properties of lake Osisko sediments, and (ii) studying the pollution that occurred within lake water due to the sedimentsâ reactivity. Water and sediments across the lake were collected in different sensitive locations. Within the sediment samples, two parts were distinguished: a small layer of black vase over grey sediments. The black vase resembled organic matter while the gray sediment seemed close to clean lake sediments. The collected samples were characterized for their physical (particle size distribution, specific gravity and specific surface area), chemical (minor and major elements as well as total sulfur and carbon) and mineralogical (X-ray diffraction and scanning electron microscope) properties. Additionally, the reactivity of sediments was studied using weathering cells to quantify chemical species leaching and their releasing rates. The results showed that the vase was the only contaminated part with high concentrations of sulfur and metals such as copper, zinc and iron. Geochemical data showed that the composite sample and the vase potentially cause contaminated acid drainage if they are exposed to atmospheric conditions. Indeed, the pH values of the leachates from both samples were between 4 and 6, while those corresponding to sediments remained around circumneutral values. Quantitatively, the contaminant release from the tested samples was variable. Indeed, the Fe cumulative concentrations were around 200, 80 and 20 mg/kg for the vase, composite and sediment samples, respectively. Similarly, the Zn cumulative concentrations were around 4500, 4200, and below the detection limit for vase, composite and sediment samples, respectively. The same tendency was observed for Cu, S, and Fe. Thus, sediments within Osisko lake present a risk for water contamination if they are resuspended or dredged out of the lake. Consequently, they should be stabilized before their disposal. The samplesâ high Cu contents also offer the possibility of their reprocessing
Towards Zero Solid Waste in the Sedimentary Phosphate Industry: Challenges and Opportunities
The phosphate industry produces huge volumes of waste (hundred million tons per year). These wastes are generally surface landfilled, leading to significant environmental impacts and a large footprint. The current practices of phosphate waste management, the typology of the waste streams and their characteristics, and finally their potential applications are reviewed. All the waste streams generated during the life cycle of phosphoric acid production going from the extraction of phosphate rock to its enrichment and transformation are considered. Great circularity opportunities have been identified and they aim (i) to recover the residual phosphorus and other critical minerals and metals, and (ii) to consider phosphate wastes as alternative resources in the civil engineering and building sectors. The purpose is to shift from linear thinking to circular thinking where synergy between different mining and other industries is highly encouraged. By doing so, opportunities to safeguard natural resources and to minimize the environmental and societal impacts are limitless. However, many challenges are still limiting this shift: economic and technical constraints, societal and policy-makersâ awareness, regulation harmonization and finally knowledge gaps. More efforts and investment in research and development are still required to reach the zero-waste target
In Situ Effectiveness of Alkaline and Cementitious Amendments to Stabilize Oxidized Acid-Generating Tailings
This study investigates the effectiveness of alkaline and cementitious additives in the in situ stabilization of localized acid-generating tailings from a closed gold mine in Abitibi−Témiscamingue, Québec (Eagle/Telbel mine site). Five field cells (including one control) were constructed and equipped with mechanisms for collecting vertical water infiltration and surface runoff. The five cells included: (C1) Control cell; (C2) 5 wt % limestone amendment; (C3) 10 wt % limestone amendment; (C4) 5 wt % half ordinary Portland cement and half fly ash amendment; and (C5) 5 wt % ordinary Portland cement amendment. The control cell showed an acidic behavior (pH < 4.5) with variable concentrations of Fe, Al, Zn, and Cu. The amendments were used to neutralize the acidic leachates and decrease dissolved metal concentrations. Leachates from surface runoff samples of amended cells were less loaded with metals compared to samples of vertical infiltration. All amendment formulations increased the pH of the leachates from approximately 4 to circumneutral values. Furthermore, metal and metalloid concentrations were greatly limited, except for Cr and As for the carbonate-based amendments. Metal(-oid) stabilization was successfully achieved using the different amendment formulations, with the exception of C2, which still released As
Alkali-Hydrothermal Treatment of K-Rich Igneous Rocks for Their Direct Use as Potassic Fertilizers
International audienceDue to the increasing demand for conventional sources of potassium (K) and their inaccessibility by African countries, K-rich igneous rocks are increasingly studied as potential alternative sources. In this study, six potassic igneous rocks (syenites and trachytes) from the Tamazeght, Jbel Boho, Ait Saoun, and El Gloâa regions (Morocco) were sampled and characterized. Then they were hydrothermally treated to enhance their K release for potential use as potassic fertilizers. The raw materials are mainly formed by microcline (up to 74%), orthoclase (20â68%), albite (36â57%), biotite-muscovite (15â23%), and titanite, calcite, hematite, and apatite as accessory minerals. These samples were crushed and milled to reach a particle size <150 ”m and mixed with 4 N NaOH solution in an autoclave. The liquid/solid (L/S) ratio was about 44 mL/50 g. The powders were allowed to react with the solution at 170 °C for 7 h. For all tests, NaOH reacted completely with the powders and no liquid was observed after the treatment. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), infrared spectroscopy (IRTF), and scanning electron microscopy (SEM-EDS) were carried out on treated samples to characterize the mineralogical and structural changes due to the alkali-hydrothermal treatment. Indeed, the treated samples revealed the presence of sodic neoformed phases such as thermonatrite, sodalite, analcime, and cancrinite. The treated material was leached for a week using deionized water and the elements released were measured using inductively coupled plasmaâatomic emission spectroscopy (ICP-AES). The hydrothermal process showed a strong effect on structure breakdown as well as on the release of K and other nutrients such as P, Fe, Si, Mg, and Ca. Therefore, the alkali-hydrothermal treatment allowed the release of 50.5 wt% K. Moreover, the release of Mg, Ca, Fe, P, K, and Si were significantly increased. Mg, Ca, Fe, P, K, and Si release within raw materials was about (0.5â3.6), (3.5â31.4), (0.01â0.4), (0.01â0.3), (20â55), and (4.6â8) mg/kg, respectively, whereas treated samples showed a higher release of these elements. Quantitatively, Mg, Ca, Fe, P, K, and Si releases were about (10â11.8), (60â70), (7â20), (1.2â15), (218â1278), and (1119â2759) mg/kg, respectively. Consequently, the treated igneous rocks (syenite and trachyte) could be directly used as potassic fertilizers that would also be a source of other nutrients
Phosphate Rocks: A Review of Sedimentary and Igneous Occurrences in Morocco
International audiencePhosphate rocks are a vital resource for world food supply and security. They are the primary raw material for phosphoric acid and fertilizers used in agriculture, and are increasingly considered to be a potential source of rare earth elements. Phosphate rocks occur either as sedimentary deposits or igneous ores associated with alkaline rocks. In both cases, the genesis of high-grade phosphate rocks results from complex concentration mechanisms involving several (bio)geochemical processes. Some of these ore-forming processes remain poorly understood and subject to scientific debate. Morocco holds the worldâs largest deposits of sedimentary phosphate rocks, and also possesses several alkaline complexes with the potential to bear igneous phosphate ores that are still largely underexplored. This paper summarizes the main geological features and driving processes of sedimentary and igneous phosphates, and discusses their global reserve/resource situation. It also provides a comprehensive review of the published data and information on Moroccan sedimentary and igneous phosphates. It reveals significant knowledge gaps and a lack of data, inter alia, regarding the geochemistry of phosphates and basin-scale correlations. Owing to the unique situation of Moroccan phosphates on the global market, they clearly deserve more thorough studies that may, in turn, help to constrain future resources and/or reserves, and answer outstanding questions on the genesis of phosphates
Highly variable content of fluorapatite-hosted CO32- in the Upper Cretaceous/Paleogene phosphorites (Morocco) and implications for paleodepositional conditions
International audienc
Deciphering the U-Pb dates of sedimentary phosphates: A complex example from the Upper Cretaceous-Lower Paleogene series in northwestern Morocco
Uraniumâlead geochronology rapidly generates dates of rock deposition/formation with reasonable precision and accuracy using laser ablation inductively coupled plasma mass spectrometry, which is needed for bracketing stratigraphy. However, previous radiometric U-Pb dating of biogenic (i.e., bones and teeth) and sedimentary phosphate minerals have had limited success, probably because of the nanometric to micrometric crystallites that generate open system behavior. Sediment lithification inhibiting trace element exchange between minerals and porewaters and thus forcing phosphorus-rich crystallites to adopt a closed system behavior has been suggested for interpreting U-Pb dating of carbonate fluorapatite (CFA). Despite these insights, what remains lacking is extensive U-Pb CFA dating at the regional scale to test whether several processes influence the timing of U-Pb system closure by inhibiting U and Pb exchanges. Here, we report U-Pb CFA dating from four sampling sites in northwestern Morocco to understand better the meaning of U-Pb dates in CFA. The Upper Cretaceous-Lower Paleogene phosphate series yields anomalously low 207Pb/206Pb initial ratios and young dates ranging from 37.3 ± 2.4 Ma to 22.7 ± 0.7 Ma, which does not agree with the terrestrial lead model composition for Paleogene ages and the known biostratigraphic ages, respectively. We argue that ancient radiogenic Pb from leached polymetallic mineralizations of the regional environment have been incorporated into CFA and that a 25 to 40 Ma-long widespread resetting of the U-Pb system has affected the northwestern Moroccan phosphates. Neither CFA-hosted CO32â concentrations nor rare earth element and yttrium contents indicate post-depositional modifications of the chemical nature of phosphate-bearing rocks. Burial diagenesis promoting sediment lithification is one of the mechanisms that have triggered final closure of the U-Pb system of CFA minerals and, interestingly, the sedimentation rate was probably not a controlling factor. Unexpectedly, U-Pb dates of âŒ23 Ma from three stratigraphic levels separated by several million years seem to be concomitant with the regional emersion and generalized continentalization of northwestern Morocco, allowing CFA to behave as a closed system. We conclude that the laser ablation inductively coupled mass spectrometry U-Pb dating of biogenic and sedimentary CFA minerals must be carefully employed to date the timing of fossilization or sediment deposition
Deciphering the U Pb dates of sedimentary phosphates: A complex example from the Upper Cretaceous-Lower Paleogene series in northwestern Morocco
International audienceUraniumâlead geochronology rapidly generates dates of rock deposition/formation with reasonable precision and accuracy using laser ablation inductively coupled plasma mass spectrometry, which is needed for bracketing stratigraphy. However, previous radiometric Usingle bondPb dating of biogenic (i.e., bones and teeth) and sedimentary phosphate minerals have had limited success, probably because of the nanometric to micrometric crystallites that generate open system behavior. Sediment lithification inhibiting trace element exchange between minerals and porewaters and thus forcing phosphorus-rich crystallites to adopt a closed system behavior has been suggested for interpreting Usingle bondPb dating of carbonate fluorapatite (CFA). Despite these insights, what remains lacking is extensive Usingle bondPb CFA dating at the regional scale to test whether several processes influence the timing of Usingle bondPb system closure by inhibiting U and Pb exchanges. Here, we report Usingle bondPb CFA dating from four sampling sites in northwestern Morocco to understand better the meaning of Usingle bondPb dates in CFA. The Upper Cretaceous-Lower Paleogene phosphate series yields anomalously low 207Pb/206Pb initial ratios and young dates ranging from 37.3âŻÂ±âŻ2.4âŻMa to 22.7âŻÂ±âŻ0.7âŻMa, which does not agree with the terrestrial lead model composition for Paleogene ages and the known biostratigraphic ages, respectively. We argue that ancient radiogenic Pb from leached polymetallic mineralizations of the regional environment have been incorporated into CFA and that a 25 to 40âŻMa-long widespread resetting of the Usingle bondPb system has affected the northwestern Moroccan phosphates. Neither CFA-hosted CO32â concentrations nor rare earth element and yttrium contents indicate post-depositional modifications of the chemical nature of phosphate-bearing rocks. Burial diagenesis promoting sediment lithification is one of the mechanisms that have triggered final closure of the Usingle bondPb system of CFA minerals and, interestingly, the sedimentation rate was probably not a controlling factor. Unexpectedly, Usingle bondPb dates of ~23âŻMa from three stratigraphic levels separated by several million years seem to be concomitant with the regional emersion and generalized continentalization of northwestern Morocco, allowing CFA to behave as a closed system. We conclude that the laser ablation inductively coupled mass spectrometry Usingle bondPb dating of biogenic and sedimentary CFA minerals must be carefully employed to date the timing of fossilization or sediment deposition