Qingyou Liu

Assessing the Influence of Calcium Fluoride on Pyrite Electrochemical Dissolution and Mine Drainage pH.

We investigated the influence of dissolved calcium fluoride, CaF(aq), on the electrochemical dissolution of pyrite and the corresponding environmental effects on acid mine drainage (AMD). The experimental results showed that CaF(aq) promotes pyrite electrochemical dissolution. When the CaF(aq) concentration increased from 0 to 10 mg L up to saturation, the promoting efficiency was 15.80 and 57.25%, respectively. The reason for this phenomenon is that F and Fe form FeF, and at a higher scan potential, F and Fe form the ion complex FeF. The mechanisms include: (i) the decreasing charge transfer resistance at the double layer due to the iron fluorine complex formation; and (ii) the decreasing passivation resistance at the cover layer due to the strong penetration of F ions through it into the double layer. Although the hydrolysis reaction of F in solution could increase the pH value of mine drainage, the AMD was significantly aggravated because CaF(aq) promoted the pyrite electrochemical dissolution.

Assessing the influence of humic acids on the weathering of galena and its environmental implications

Galena weathering often occurs in nature and releases metal ions during the process. Humic acid (HA), a critical particle of natural organic matter, binds metal ions, thus affecting metal transfer and transformation. In this work, an electrochemical method combined with spectroscopic techniques was adopted to investigate the interfacial processes involved in galena weathering under acidic and alkaline conditions, as well as in the presence of HA. The results show that the initial step of galena weathering involved the transformation Pb2+ and S°, regardless of whether the solution was acidic or alkaline. Under acidic conditions, S° and Pb2+ further transform into anglesite, and HA adsorbs on the galena surface, inhibiting the transformation of sulfur. HA and Pb (II) ions form bridging complexes. Under alkaline conditions without HA, the sulfur produced undergoes no transformation, whereas Pb2+ will transform into PbO. The presence of HA changes the galena weathering mechanism via ionization effect, and Pb2+ is ultimately converted into anglesite. Higher acidity in acidic conditions or higher alkalinity in alkaline conditions causes galena corrosion when the electrolyte does not contain HA. Conversely, higher pH always accelerates galena corrosion when the electrolyte contains HA, whether the electrolyte is acidic or alkaline. At the same acidity/alkalinity, increasing the concentration of HA inhibits galena weathering. Galena will release 134.7 g m-2·y-1 Pb2+ to solution at pH 2.5, and the amount decreases to 28.09 g m-2·y-1 in the presence of 1000 mg/L HA. This study provides an in situ electrochemical method for the assessment of galena weathering.