Recycling of mine wastes as raw materials for the construction sector: Solutions based on materials circularity and sustainable resource governance

The mining industry in general, and the phosphate industry in specific is an important mainstream in terms of waste rocks as it generates huge amounts of waste rocks and tailings during their activities. As a matter of example, the phosphate mining in Morocco produces amounts up to 150 million tons or even more of waste rocks and tailings each year. Non-polluting mine wastes (Tailings and waste rock) must be regarded as an opportunity to create new value. The reuse of these wastes, depending on their chemical, mineralogical and geotechnical properties, as alternative raw material in construction and building materials field constitutes a promising environmental solution. The main objective of our studies in Morocco was to investigate the feasibility of using non-polluting mine wastes to produce materials especially for the construction sector, such as using phosphate mine wastes as cementing materials, as additives in mortars or concrete, or as raw materials for bricks, ceramics and geopolymers or aggregates for roads construction and B25 concrete. The phosphate waste rock has to be classified in the category of natural aggregates that are similar to conventional materials. Laboratory and pilot scale investigations demonstrated that recycling mine wastes from may be feasible. The presentation will be focused mainly will be focused mainly on the valorization of phosphate waste rock an alternative aggregate in the construction sector. In addition, Jerada coal mine wastes recycling investigate the use of an integrated and circular approach based on coal recovery and waste rock recycling as alternative clays and aggregates (gravel and sand) in the construction sector. Froth flotation was used to recover coal particles using diesel as a collector and Methyl Isobutyl Carbinol as a frother. The tailings of coal flotation process (CFT) were used to manufacture fired bricks at a pilot scale. Then, gravel and sand obtained after a CMWR screening were tested as alternative materials for concrete production. The choice of the construction sector is based on its capacity to absorb huge quantity of materials

Evaluation of the effect of sodium silicate addition to mine backfill, Gelfill − Part 1

In this paper, the mechanical properties of sodium silicate-fortified backfill, called Gelfill, were investigated by conducting a series of laboratory experiments. Two configurations were tested, i.e. Gelfill and cemented hydraulic fill (CHF). The Gelfill has an alkali activator such as sodium silicate in its materials in addition to primary materials of mine backfill which are tailings, water and binders. Large numbers of samples of Gelfill and CHF with various mixture designs were cast and cured for over 28 d. The mechanical properties of samples were investigated using uniaxial compression test, and the results were compared with those of reference samples made without sodium silicate. The test results indicated that the addition of an appropriate amount of an alkali activator such as sodium silicate can enhance the mechanical (uniaxial compressive strength) and physical (water retention) properties of backfill. The microstructure analysis conducted by mercury intrusion porosimetry (MIP) revealed that the addition of sodium silicate can modify the pore size distribution and total porosity of Gelfill, which can contribute to the better mechanical properties of Gelfill. It was also shown that the time and rate of drainage in the Gelfill specimens are less than those in CHF specimens made without sodium silicate. Finally, the study showed that the addition of sodium silicate can reduce the required setting time of mine backfill, which can contribute to increase mine production in accordance with the mine safety

Evaluation of the effect of sodium silicate addition to mine backfill, Gelfill – Part 2: Effects of mixing time and curing temperature

The effects of mixing time and curing temperature on the uniaxial compressive strength (UCS) and microstructure of cemented hydraulic fill (CHF) and sodium silicate-fortified backfill (Gelfill) were investigated in the laboratory. A series of CHF and Gelfill samples was mixed for time periods ranging from 5 min to 60 min and cured at temperatures ranging from 5 �Cto 50 �C for 7 d, 14 d or 28 d. Increasing the mixing time negatively influenced the UCS of Gelfill samples, but did not have a detectable effect on CHF samples. The curing temperature had a strong positive impact on the UCSs of both Gelfill and CHF. An elevated temperature caused rapid UCS development over the first 14 d of curing. Mercury intrusion porosimetry (MIP) indicated that the pore size distribution and total porosity of Gelfill were altered by curing temperature

Mix proportioning of underground cemented tailings backfill

The usage of cemented tailings backfill (cemented paste backfill) in the underground by mining industry is becoming increasingly important. However, until now, the mix proportioning of CTB has been mainly based on the realization of extensive laboratory tests on a large number of CTB mixes. Therefore, this paper presents a design method for mix proportioning of CTB to minimize the number of trial mixes and provide an appropriate mix proportion. This method is based on the pairing of the response surface method (RSM) and the desirability approach. First, the RSM was used to develop predictive models for the performance properties of CTB. The predicted properties in question are the uniaxial compression strength (UCS), the slump, the solid concentration (solid percent, %Solid) and the cost (based on cement cost) of the CTB. The predictive models that were developed were able to accurately represent the relationships between the physical and chemical characteristics of the CTB components (tailings, binder, water) and the above properties. The results of the modeling phase were then used as input data in the optimization phase (based on desirability approach) to develop optimal recipes for the studied CTBs. This study has demonstrated that the combination of the RSM and desirability approach represents an effective tool for CTB mix proportioning. It has also shown that the mix parameters (cement content, water-to-cement ratio, tailings fineness and density) affect the performance properties of CTB. The results of this research provide a more comprehensive engineering approach to CTB mix proportioning. The developed design method can be useful in reducing the laboratory test protocol needed for the determination of the optimal mix composition. (c) 2006 Elsevier Ltd. All rights reserved

Laboratory Evaluation of the Use of Alkaline Phosphate Wastes for the Control of Acidic Mine Drainage

Pyrrhotite tailings at the abandoned Kettara mine site in Morocco are producing acid mine drainage (AMD). We investigated the use of alkaline phosphate waste (APW) rock from a nearby operating open-pit phosphate mine to control the AMD. The neutralizing potential of the APW, using the Paktunc method, was estimated between 500 and 680 kg CaCO3/t. In laboratory column tests, the addition of 15 wt% APW to the coarse Kettara tailings produced leachates with significantly lower acidities and metal concentrations than unamended controls. The high calcium concentration in the flushed solutions indicates that calcite was responsible for the neutralization. Dolomite dissolution seems to be negligible and fluorapatite was stable under the testing conditions. It was also observed that when the treated solution comes in contact with unweathered Kettara coarse tailings, the pH becomes acidic, although the metal concentrations remain low

Badania fizykochemiczne i mechaniczne właściwości skonsolidowanych i nieskonsolidowanych zawiesin nasyconych cementem

W ostatnich latach obserwuje się, że wydajność i jakość próbek zawiesin nasyconych cementem (CPB – Cement Paste Backfill) in situ są stale niższe niż tych samych próbek przygotowanych w plastikowych formach w laboratorium. Może to wynikać z braku w laboratorium skutecznego narzędzia mogącego naśladować zawiesiny in situ, warunki ich utwardzania jak również rozmiary i geometrię próbek. W celu wypełnienia tej luki, w laboratorium opracowano nowe narzędzie o nazwie CUAPS (Curing Under Applied Pressure System), wytworzone i wykorzystane do zbadania wpływu ciśnienia na podstawie skutecznego nacisku na właściwości fizykochemiczne i mechaniczne CPB, jak również próbek otrzymanych z plastikowych form. Badania porównawcze przeprowadzono zarówno dla próbek CUAPS jak i próbek otrzymanych w laboratorium, zawierających lepiszcza (cementu) 3,45 i 7% wag. po 7, 14 i 28 dniach utwardzania. Wyniki wskazują, że wydajność próbek konsolidowanych CUAPS są zawsze bardziej prawdziwe (realistyczne) niż próbek otrzymanych w laboratorium, głównie z powodu odprowadzania wody w wyniku konsolidacji. Ostatecznie metoda CUAPS powoduje korzystny wpływ na utwardzenie CPB dzięki zawartości wody (separacja wody od świeżej zawiesiny odpadów z cementu) i połączeniu części wody zasobowej z zawiesiną w zrobach.In recent years, it has been observed that the performance and quality of in situ cemented paste backfill (CPB) samples are constantly lower than samples obtained from the same CPB mix poured into laboratory-prepared plastic moulds. This could be well explained by the absence of an efficient laboratory tool capable of mimicking CPB’s in situ placement, hardening, and curing conditions relating to stope size and geometry. To meet this need, a new laboratory tool named CUAPS (curing under applied pressure system) was manufactured and used to examine the effect of curing under effective stress on physico-chemical and mechanical properties of CPB, along with plastic mould samples. A comparative study was conducted for both CUAPS and mould samples containing a binder content of 3, 4.5, and 7 wt% after curing times of 7, 14, and 28 days. Results indicate that the performance of CUAPS-consolidated samples are always more realistic than those of plastic mould-unconsolidated samples mainly due to water drainage induced by consolidation. CUAPS has witnessed an advantageous effect on CPB hardening which includes the amount of bleeding water (separation of water from the fresh backfill material) and a combination of drainage of part of the mixing water and the settlement of paste backfill after its placement in the cap

Parametry jednowymiarowej konsolidacji podsadzki w postaci cementowej pasty

Each year, mine and mill operations generate enormous amounts of two waste types - fine-grained tailings and coarse-grained waste rocks. Fine-grained tailings are either discharged in slurry form to surface tailings dams or delivered in cementitious form to underground mine stopes as backfilling, while coarse-grained rocks are typically stored by depositing as a dry material in large dumps. The engineering design of surface tailings dams or underground mine stopes is often controlled by the high compressibility and low shear strength characteristics of fine-grained tailings. Cemented paste backfill CPB indicating saturated, fine-grained backfills can undergo major consolidation settlement during early curing stages. Thus, a better understanding of the rate and magnitude of both differential and total settlement of CPB cured under stress is essential for a proper backfill geotechnical design. The consolidation parameters of CPB can be determined from an improved lab setup called CUAPS (curing under applied pressure system). This setup is capable of simulating the CPB placement and curing conditions, and measuring the consolidation parameters of CPB cured under effective stresses ranging between 0.5 and 400 kPa. In this study, a series of one-dimensional consolidation tests were conducted on CPB samples allowing for examination of the effects of binder type and rate as well as curing time on the compression properties (e.g., coefficient of consolidation cv, compression index Cc, and recompression index Cr) and the final geotechnical index properties (e.g., void ratio ef, water content wf, and degree of saturation Sf). Results showed that as the binder content increases, the initial resistance to consolidation increases. The cv value decreases over the course of time due to evolution of the CPB microstructure generated by the hydration process.W procesach pozyskania i przeróbki węgla powstają duże ilości odpadów dwóch rodzajów: drobnoziarniste odpady (muły) i gruboziarniste - odpady skały płonnej. Odpady drobnoziarniste (muły) są odprowadzane jako zawiesina na stawy osadowe lub kierowane są do wypełnienia zrobów w podziemiach kopalń, natomiast odpady gruboziarniste zazwyczaj są składowane w postaci suchego materiału na hałdach. Składowiska tych odpadów, zarówno powierzchniowe jak i podziemne, wymagają częstych kontroli ze względu na dużą kompresję (ściśliwość) oraz płynięcie (ścinanie). Drobnoziarniste odpady nasycone cementem CPB (Cement Paste Backfill) mogą we wczesnych stadiach utwardzania ulegać konsolidacji w procesie osiadania w zrobach. Aby przygotować odpowiednią mieszaninę do wypełnienia zrobów konieczna jest dobra znajomość całkowitej wielkości i różnic w osiadaniu CPB utwardzanych w warunkach ciśnienia. Parametry konsolidacji CPB mogą być badane w warunkach laboratoryjnych z wykorzystaniem ulepszonego zestawu aparaturowego o nazwie CUAPS (Curing Under Applied Pressure System) - utwardzanie pod ciśnieniem. Taka konfiguracja jest w stanie symulować warunki utwardzania CPB, a więc pomiar parametrów konsolidacji przy efektywnych naprężeniach w zakresie od 0,5 do 400 kPa. W tym przypadku, seria jednowymiarowych prób konsolidacji prowadzona była na próbkach PCB, umożliwiających zbadanie wpływu rodzaju spoiwa i czasu utwardzania na właściwości kompresji (np. współczynnik konsolidacji Cv, wskaźnik kompresji Cc i wskaźnik dekompresji Cr) oraz końcowe właściwości geotechniczne (np. wskaźnik porowatości ef, zawartość wody wf i stopień nasycenia Sf). Wyniki pokazują, że ze wzrostem zawartości spoiwa, wzrasta odporność na konsolidację. Wartość współczynnika konsolidacji cv maleje w miarę upływu czasu w wyniku zmiany mikrostruktury CPB wywołanej hydratacją