Geochemical Association of Ni2+, Zn2+, Pb2+, Ag+, Cu2+, and Co2+ Ions in Natural Pyrite

The natures of competitive adsorption of six metal ions on the natural pyrite surface have been studied with an objective to provide strong foundations towards mode of association/occurrence of trace elements on pyritic surface. Some parameters, for instance, adsorption edge, mechanism, correlation coefficient, monolayer coverage, pH, and thermodynamic parameters, have been considered here. The significant results are the order of increasing trend of adsorption edges which has been found to be Pb2+ < Cu2+ < Ni2+ < Zn2+ < Co2+ < Ag+. Nonuniformity in variation of adsorption edge of a particular metal ion in presence of a second metal ion in solution is evident from the study. However, in case of Ag2+ and Co2+ ions two adsorption edges are observed. These variations have been explained based on the formation of hydroxo complexes which are pH dependent. The competitive monolayer coverage of each metal ion as a function of pH has shown variation in the extent of adsorption. Computed higher correlation coefficient in a binary system indicates retardation in adsorption of metal ion in presence of a second metal ion. Further the adsorption of metal ions on pyrite surface showed exothermic processes due to the spontaneous nature at low temperature. Our study has strongly revealed promising adsorbent characteristics of natural pyrite with considerable geochemical and environmental implications. 1. Introduction Water discharged by industrial activities and from mines is often contaminated by a variety of harmful substances including metal ions [1–5] which have a deleterious effect on the water environment. To remove the harmful metal ions from polluted water, it is quite essential to precisely understand the method of purification of water. Much effort is being expended in the development of several processes for production of clean water. Application of activated carbon for the removal of metal ions from aqueous phase by adsorption is largely known [1–5], but competitive adsorption of metal ions on natural pyrite surface is limited. To study the adsorption characteristics, it is prerequisite to know the nature of association of various metal ions on the sulphide minerals. Association of inorganic elements in the coal organic matter and their extent of incorporation have been reported [6–12]. In regard to minerals, calcite, dolomite, siderite, and so forth are the carbonate minerals while pyrite and/or marcasite is the well-known sulphide minerals [13]. According to Miller and Given [14], jarosite and goethite are often encountered as natural weathering processes