Abstract
This work seeks to assess the acid mine drainage (AMD) potential of stockpiled sulphidic gold bearing ore that was left untreated for a period of four (4) years. The mineralogical composition of the stockpiled sulphidic gold ore was determined using X-Ray Diffractometry (XRD) and Reflected Light Microscope. The AMD potential and kinetic studies on the ore sample were determined using Acid Base Accounting (ABA) and Humidity Cell (ASTMD 5744). The XRD and microscope analyses showed that the gold ore contain arsenopyrite and pyrite as the major sulphide minerals. The ABA confirmed that the gold sulphide ore could be a potential source of AMD with respect to AMD marginal of safety if the ore is left untreated for a very long period. Humidity Cell kinetic analysis showed a possibility of mobilizing Arsenic (As) into the geo-environment when there is a long period of oxidation of abandoned sulphide run-of-mine (ROM) ore.
Highlights
Natural geochemical processes that oxidize metal sulphides exposed at the earth’s surface by anthropogenic activities such as mining, results in acid mine drainage (AMD)
The mineralogy of the Run of Mine (ROM) ore was determined by using physical observation, reflected-light microscopy (RLM) and X-ray diffractometry (XRD)
The mineralogical analysis carried out on the gold ore showed that arsenopyrite and pyrite are the most common sulphide minerals present in the stockpiled material
Summary
Natural geochemical processes that oxidize metal sulphides exposed at the earth’s surface by anthropogenic activities such as mining, results in acid mine drainage (AMD). Iron and sulphur oxidizing bacteria are known to catalyze these reactions at low pH thereby increasing the rate of reaction by several orders of magnitude (Nordstrom and Southam, 1997). These reactions occur naturally but at a rather slow rate. The reaction of pyrite with oxygen and water produces a solution of ferrous ion (Fe2+), sulphate ion (SO42-) and protons (H+ acid) (Jennings et al, 2008; Simate and Ndlovu, 2014). The chemical characteristics associated with AMD are low pH values (high acidic water), high concentration of metals (iron, aluminium and manganese and other heavy metals) and metalloids (of which arsenic is generally of great concern) and sulphate ions in solution (Johnson and Hallberg, 2005; Mendez-Ortiz et al, 2007)
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