FCT; European Social Funds of MCTESinfo:eu-repo/semantics/publishedVersio

Cordeiro, Mayara

Gomes, Patrícia

Grande, José António

Valente, Teresa Maria Fernandes

Universidade do Minho: RepositoriUM

XII CONGRESO NACIONAL Y XI IBÉRICO DE GEOQUÍMICAInvestigar los recursos cuidando el ambienteLinares (Jaén), 26 a 28 septiembre 2017114RELATIONSHIPS BETWEEN PHYSICO-CHEMICAL INDICATORSOF ACID MINE DRAINAGEGomes, Patríciaa, Valente, Teresab, Grande, José Antónioc, Cordeiro, Mayarada Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, email: fpssgomes@gmail.comb Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, email: teresav@dct.uminho.ptc University of Huelva & Escuela Técnica Superior de Ingeniería, Spain, email: grangil@uhu.esd Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, email: mayaratcordeiro@gmail.comABSTRACTAcid mine drainage (AMD) is an important focus of environmentimpact that supports the degradation of the ecosystems at globallevels. São Domingos mine is a paradigmatic site in thePortuguese Iberian Pyrite Belt, known by strong contaminationby AMD. The acidic waters drain into the Chança water dam,highlighting the importance of the mine regardingaccomplishment of water quality compatible with humanconsumption.The present study shows the variations between pH, ElectricalConductivity, Total Acidity and Sulphates in the rainy season(from October to March 2017) in the most affected areas, aswell as the response of the receiving water dam to the changesinduced by AMD.The results indicated that the extreme values occur in onepeculiar small dam (PAT 7), as result of AMD potential of theaccumulations of very fine grain sulfide-rich wastes that draininto this dam. Here, strong reactivity is marked by waterphysical-chemical parameters as well as by the presence ofmineralogical indicators, such as salt efflorescences. Thecorrelation between parameters reflects water-mineralinteractions involving the sulfides, which oxidative dissolution isresponsible for the production of acid sulphate waters.Key words: physical-chemical, total acidity, sulphates, acid minedrainage, São Domingos mine.1. INTRODUCTIONSince pre-historic times, the humankind explores natural resour-ces to obtain raw materials. The exploitation of mineral resour-ces stimulates the economy, creates wealth, but generatesimpacts that may be the basis of some conflicts of interest withother uses of the territory. The mining industry is one of the mostproblematic activities in the primary sector. This impact is evensuperior in mines whose abandonment occurred in an uncontro-lled manner, generating environmental focus that persists untiltoday (Gomes, 2011). Sulfide-rich waste-dumps, when exposed to weathering proces-ses, promote a global environmental problem related with acidmine drainage (AMD) (Chockalingam and Subramaniam, 2009).In the rainy season, waters interact with sulfide materials in thewaste-dumps and release acidity, sulphate and metals, formingacid sulphate-rich leachates (Grande et al., 2016). In the Iberian Pyrite Belt (IPB) there are many abandoned minesthat do not present any corrective or preventive measures forthe aquatic system. São Domingos mine is located in thePortuguese sector of the IPB, and it was an important miningcentre dating back to pre-Roman times remaining in activity until1966, when it was definitely halted (Álvarez-Valero et al., 2008).It is characterized by an open pit exploitation of massive sulfideores that are located near the top of the Volcanic SedimentaryComplex. Nowadays, the waste-dumps are spread along appro-ximately 5.5 km in the margin of the Chança River, being themain contaminant focus of the water system. Inserted in thesemi-arid climate of this area and considering the lack of waterresources in this region (Alentejo), the study of AMD contamina-tion is a relevant issue.The specific objectives of the present work are focused on cha-racterizing the variations between pH, Electrical Conductivity,Total Acidity and Sulphates in the rainy season (from October toMarch) and observing the response of the aquatic system to thechanges induced by AMD. This will give indication about the de-gree of contamination in São Domingos and will allow prelimi-nary understanding of the hydrochemical and hydrologicalrelationships that are occurring in the receiving aquatic system(Chança reservoir, used human consumption). Sampling pointswere selected immediately upstream and downstream of SãoDomingos mine, in order to evaluate the effects of the leachateson the physical-chemical parameters of the system.2. MATERIALSField sampling and laboratory analyses implied the use of diverseequipment, materials and reagents. Multiparameter portablemeter CRISON MM40+ was used for in situ parameters. The follo-wing Orion probes were used: combined pH/ATC electrode Trioderef. 91-07WM and a conductivity cell DuraProbe ref. 013010.Potential redox (Eh) was measured using multiparameter porta-SESIÓN 3. MÉTODOS MATEMÁTICOS Y ANALÍTICOSRelationships between physico-chemical indicators of acid mine drainagewww.congresodegeoquimica.orgin water dams along the mining complex (PAT 3-PAT 9); upstreamof the confluence in the Chança river (PAT 10); in the plume ofAMD dispersion (PAT 11), and in the Chança water dam (PAT 12). Field determinations presented in this work consisted in the follo-wing parameters: pH, Electric Conductivity (EC) and Potential Redox(Eh). In the laboratory, Total Acidity was immediately measuredby volumetric determination (ASTM, 1992), whereas sulphateswere determined by turbidimetry (Standard Methods, 4500 E).Samples of efflorescent salts were collected in March with plasticspatulas in closed polyethylene bottles around de sampling pointPAT 7 (Fig. 1). X-ray diffraction (XRD) and scanning electron mi-croscopy were applied for their mineralogical analysis.4. RESULTS AND DISCUSSIONTable 1 shows the results of water parameters. The pH shows variability among water dams. As expected, thehighest value (7.52) was found in the water dam referenced asPAT 1, in January 2017. This sampling point represents cleanwater, without influence of the acid leachates. Therefore, it hasthe highest pH range, from 5.18 to 7.52. In a similar way, PAT 12presents also high pH values, showing the absence of contami-nation in a location already far from the mine. The lowest valuewas 1.44 (PAT 7), measured in October 2016, highlighting theeffect of AMD from the sulfide wastes accumulated around themetallurgical complex. Furthermore, this dam (PAT 7) shows uni-que conditions regarding evidences of reactivity and mining po-llution. This fact can be explained by the high contaminationpotential of several waste-dumps and piles that drain into PAT 7.From mineralogical and textural point of view, the analyses re-flect the purity of these materials, which are mainly composed bymilled pyrite and chalcopyrite, describing a typical scenario ofpolymetallic sulfides from volcanic-hosted massive deposits(Grande et al., 2013). Moreover, strong salinization is anotherevidence of reactivity. It is possible to observe over the wastedumps, pools and banks of the drainage channel, a variety of co-lours promoted by the blooms of salt efflorescences. Figure 2shows the PAT 7 surrounding area and the soluble salts. In humidmicroenvironments, melanterite (FeSO4. 7H2O) is the most abun-dant phase. Additionality, analysis performed by XRD allowed theidentification of sulfate minerals, such as ferricopiapite (Fe3+5(SO4)6O(OH) · 20H2O), pickeringite (MgAl2(SO4)4 22H2O), coquim-bite (Fe3+2(SO4)3·9(H2O)), as well as sulphur. These minerals areknown by their environmental importance in monitoring pollu-tants in contaminated environments (Valente et al., 2013).Samples from PAT 2 to PAT 9 have always pH < 3 in the four in-itial campaigns. The lowest pH value was recorded in PAT 5 inOctober (2.33) and PAT 4 in November (2.54). These results re-present the influence of waste dumps and meteorological con-ditions in the water quality.EC behaves somewhat inversely to pH. So, the clear water dam hadthe highest pH of all samples, while the EC was one of the lowest(28.00 S/cm in January). The highest EC occurs in the AMD solu-tions, reaching 26200 S/cm (PAT 7), in November 2016. Thus, pHand EC present the expected pattern taking in account the environ-ment of each sampling point. Downstream, from the point of theplume dispersion of AMD in the river, there is a tendency to incre-115ble meter Thermo Scientific Orion with a probe Orion triode lowmaintenance ref. 9179BN. Water samples were collected intohigh-density polyethylene containers and maintained in a porta-ble refrigerator. In the laboratory, heating plates, glass calibratedmaterial, and pro analysis reagent standard solutions were usedfor volumetric determinations in accordance with ASTM (1992). 3. METHODSThe samples were collected in different sites, as represented inFigure 1: water dam upstream the mine (PAT 1); pit lake (PAT 2);Figure 1 - Map location of water dams in São Domingos minewith sampling sitesXII CONGRESO NACIONAL Y XI IBÉRICO DE GEOQUÍMICAInvestigar los recursos cuidando el ambienteLinares (Jaén), 26 a 28 septiembre 2017116Samples pH EC (S/cm) Eh (mV) Acidity (mg/L CaCO3) SO4 (mg/L) PAT 1 Average 6,54 227,6 239 n.a. 6,6Median 6,54 264,8 271 n.a. 6,5Min 5,18 28,00 49 n.a. 2,2Max 7,52 308,0 352 n.a. 12,5PAT 2 Average 2,55 6597,2 537 3704,2 5792,6Median 2,56 7440,0 541 3820,0 5768,4Min 2,42 741,00 506 3125,0 4742,0Max 2,67 8572,0 565 4150,0 6520,2PAT 3 Average 2,67 2414,7 521 1067,5 1379,7Median 2,69 2550,0 519 938,8 1160,9Min 2,40 228,00 501 530,0 661,5Max 2,79 4251,0 543 1952,5 2661,1PAT 4 Average 2,69 2266,2 550 1311,3 1714,0Median 2,63 2334,5 552 1335,0 1824,9Min 2,54 310,00 487 437,5 552,3Max 2,99 4230,0 605 1980,0 2600,4PAT 5 Average 2,64 3018,5 5445 1847,6 2350,9Median 2,67 2880,0 535 1331,3 1606,3Min 2,33 251,00 497 640,5 865,7Max 2,84 6541,0 600 4970,0 6518,0PAT 6 Average 3,02 1456,6 509 1055,8 1083,8Median 2,81 304,00 515 702,5 660,8Min 2,71 117,30 450 0,0 68,2Max 3,99 4320,0 541 3455,0 2955,1PAT 7 Average 1,97 13387,8 531 79843,8 74077,0Median 2,13 12332,5 516 30468,8 25459,9Min 1,44 1252,0 447 11812,5 10123,7Max 2,29 26200,0 657 292500,0 282924,9PAT 8 Average 3,10 2251,5 463 1415,8 1646,7Median 2,85 1917,5 480 791,3 951,0Min 2,45 181,90 288 0,0 58,5Max 4,71 6114,0 549 4485,0 5502,6PAT 9 Average 2,98 1593,8 482 748,8 926,1Median 2,87 1436,5 478 842,5 1096,5Min 2,66 204,00 374 58,3 110,4Max 3,52 3186,0 561 1332,5 1641,5PAT 10 Average 3,19 2106,5 470 735,9 1451,7Median 3,25 956,00 466 284,6 422,9SD 0,48 3217,3 65 1148,2 2608,0Min 2,54 185,70 363 92,3 151,3Max 3,74 8598,0 543 3037,5 6753,2PAT 11 Average 3,95 544,9 386 165,7 324,6Median 3,72 370,3 426 81,3 124,4Min 2,92 168,7 85 0,0 98,4Max 5,09 1429,0 516 522,5 790,0PAT 12 Average 5,90 252,3 297 n.a. 38,3Median 5,91 248,0 310 n.a. 39,0Min 5,34 26,50 174 n.a. 26,2Max 6,58 503,1 391 n.a. 48,2TABLE 1- PHYSICAL-CHEMICAL PARAMETERS, TOTAL ACIDITY AND SULPHATE CONCENTRATION (N=6). NOT APPLICABLE= N.ASESIÓN 3. MÉTODOS MATEMÁTICOS Y ANALÍTICOSRelationships between physico-chemical indicators of acid mine drainagewww.congresodegeoquimica.orgase the pH and decrease of EC, due to dilution of the AMD andminor presence of waste dumps. The lowest EC value was found inthe Chança water dam (26.50 S/cm), in January 2017. The Figure 3 highlights the inversely relationship between pH andEC, i.e., when the EC presents extreme high values, pH is foundto have low values. In relation to sulphate concentrations, it ispossible to notice a similar trend to parameters such as TotalAcidity and EC. On the other hand, they decrease with the incre-ase of pH. As noticed for other parameters, sulphate is also highest at PAT7, with 282925 mg/L. In the opposite, PAT 1 exhibited the lowerconcentration with 2.20 mg/L, followed by PAT 12 with 26.2mg/L. Regarding the redox conditions, PAT 1 and PAT 12 presentthe lowest Eh values, in accordance with the highest pH measu-red in all campaigns.According to Grande et. al. (2017), the solubility of substances isdetermined by the acidity of the channel, as the pollutant con-centration follows the pattern defined by the values of pH, co-rresponding points with higher concentration of pollutants withthose of lowest pH values.The description of the process that happens along the system canbe as following: rainfall promotes the release of elements in thewaste dumps, generating AMD contaminated leachates causinga decrease of pH and an increase of sulphates’ concentration inthe receiving waters.In terms of the degree and type of mining pollution, climate con-ditions especially precipitation, are the most significant externalcontrolling factors (Santisteban et al., 2015).Correlation analysis provides an effective way to reveal the rela-tionships between physical parameters. Therefore, Figure 4shows the correlation between pH x Total Acidity, pH x Sulphateand Total Acidity x Sulphate, suggesting a close association.Person correlation indicated strong positive correlation of 0,907;0,862 and 0,998, respectively, highlighting the role of sulfides inthe acidity production. 5. CONCLUSIONThe preliminary results obtained for the São Domingos miningcomplex represent the influence of the mining infrastructures inthe water contamination. The sampling point that has the lowestpH was PAT 7, contrarily to PAT 1, with higher values. In general,all the extreme values were observed in PAT 7 as result of AMDproduced by the weathering of very fine grain sulfide-rich was-tes dispersed around the area. The secondary paragenesis, re-presented by sulphate efflorescences are mineralogical indicatorsof such contamination.The pH x Total Acidity, pH x Sulphate and Total Acidity x Sulphateare well correlated. This reflects the water-mineral interactions in-volving the sulfides, which oxidative dissolution is responsible forthe production of acid sulphate waters. It is possible to notice a dilution of AMD downstream, mainlyfrom the confluence with the Chança River. The meteorological conditions and the influence of waste-dumpshad a massive effect on contamination. The abandoned waste-dumps and piles continue to product acid leachates when thestructures are exposed to precipitation. Further studies intend to characterize in more detail the correlationsbetween the composition of the waste dumps, hydrological varia-tions and the hydrochemistry of water, including the response of the117Figure 2 – Image of PAT 7 surrounded by waste-dumps and piles and the presence of soluble salts at the banks of dam. Green color isdue to melanterite (FeSO4 7H2O).Figure 3 – Monthly variation of pH and EC.Chança River. These studies may help the establishment of preven-tive and rehabilitation measures for this mining complex. 6. ACKNOWLEDGMENT Patrícia Gomes wishes to acknowledge FCT (Science and TechnologyFoundation, Portugal) by the research fellowship under the POCH(Programa Operacional Capital Humano) supported by the EuropeanSocial Fund and National Funds of MCTES with referenceSFRH/BD/108887/2015. This work was co-funded by the EuropeanUnion through the European Regional Development Fund, based onCOMPETE 2020 (Programa Operacional da Competitividade eInternacionalização), project ICT (UID/GEO/04683/2013) with re-ference POCI-01-0145-FEDER-007690 and national funds providedby FCT (Science and Technology Foundation, Portugal).7. REFERENCES- Álvarez-Valero, A.M., Pérez-López, R., Matos, J.X., Capitán,M.A., Nieto, J.M., Saez, R., Delgado, J., Caraballo, M. (2008).Potential environmental impact at São Domingos mining dis-trict (Iberian Pyrite Belt, SW Iberian Peninsula): evidence froma chemical and mineralogical characterization. EnvironGeololgy. 55, 1797–1809. - ASTM 5245. (1992). Standard practice for cleaning laboratoryglassware, plasticware and equipment used in microbiologicalanalysis. ASTM Committee on Standards. American Society forTesting and Materials, 5.- AWWA, "Standard Methods for the Examination of Water andWastewater", American Public Health Association, WashingtonDC, 18th ed., 1992.- Chockalingam, E., Subramaniam, S. (2009). Utility ofEucalyptus tereticornis (Smith) bark and Desulfotomaculum ni-grificans for the remediation of acid mine drainage.Bioresource Technology 100, 615-621.- Grande, J.A., Valente T., de la Torre M.L., Santisteban, M.,Ceron, C., Pérez Ostalé, E. (2014). Characterization of acid minedrainage sources in the Iberian Pyrite Belt: base methodologyfor quantifying affected areas and for environmental mana-gement. Environ Earth Sci 71:2729-2738.- Grande, J.A., de la Torre M.L., Valente T., Pérez Ostalé, E.(2016). Spatial evolution of an AMD stream in the IberianPyrite Belt: process characterization and control factors on thehydrochemistry. Hydrological Sciences Journal. 61(8) 1503-1511.- Grande, J.A., Santisteban, M., Valente T., de la Torre M.L.,Gomes, P. (2017). Hydrochemical characterization of a riveraffected by acid mine drainage in the Iberian Pyrite Belt.Water Science & Technology. DOI: 10.2166/wst.2017.097.- Gomes, P., (2011). Processos de reabilitação natural em es-combreiras de minas abandonadas – Estudo de Casos. Tese deMestrado. Univ. Porto, Porto, 121.- Santisteban, M., Grande, J.A., de la Torre, M.L., Valente, T.,Ceron, C. (2015). Acid mine drainage in semi-arid regions: theextent of the problem in the waters of reservoirs in the IberianPyrite Belt (SW Spain). Hydrol. Res. 46, 156e167. - Pérez-Sirvent, C.; Hernández-Pérez, C.; Martínez-Sánchez, M.J.;García-Lorenzo M.L.; Bech, J. (2016) Geochemical characteri-sation of surface waters, topsoils and efflorescences in a his-toric metal-mining area in Spain. Journal of Soils andSediments, 16:1238–1252, DOI 10.1007/s11368-015-1141-3.- Valente, T.; Leal Gomes, C. (2009). Occurrence, properties andpollution potential of environmental minerals in acid minedrainage. Science of the Total Environment, 407:1135-1152.- Valente, T.; Grande, J.A.; de la Torre, M.L.; Santisteban, M.;Cerón, J.C. (2013). Mineralogy and environmental relevanceof AMD-precipitates from the Tharsis mines, Iberian Pyrite Belt(SW, Spain). Applied Geochemistry, 39:11–25.XII CONGRESO NACIONAL Y XI IBÉRICO DE GEOQUÍMICAInvestigar los recursos cuidando el ambienteLinares (Jaén), 26 a 28 septiembre 2017118Figure 4 - Correlation between pH, Total acidity and Sulphate.Pearson correlation coefficients are provided in the graphs.

Relationships between physico-chemical indicators of acid mine drainage

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Relationships between physico-chemical indicators of acid mine drainage

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