Dissolution of mimetite Pb₅(AsO₄)₃Cl in malic acid solutions

Abstract

Mimetite Pb5(AsO4)3Cl is the most insoluble lead arsenate mineral and could be used in remediation techniques to reduce As(V) mobility in soils. However, low-molecular-weight organic acids such as malic acid increase its solubility. The effect of malic acid on the dissolution of mimetite strongly depends on the pH of the equilibrium solution. At low pH, mimetite is decomposed mostly by the mechanism of protonation. With increasing pH, the solubility of mimetite decreases and a greater influence in its dissolution is ascribed to complexation of Pb(II) by organic ligands. During dissolution experiments, the amount of arsenic released to solution was > 26% higher in organic solutions than in inorganic solutions, and the amount of lead was > 8% greater. The solubility product of mimetite (KSP) was calculated in order to quantify the thermodynamic stability of the investigated mineral. The value obtained, i.e., -24.52 ± 0.49 fluctuates between the values of -21.69 ± 1.05 and -27.87 ± 0.42 reported in the literature.

EFFECT OF pH, MINING TAILINGS CONCENTRATION AND CULTURE MEDIUM ON THE PERFORMANCE OF POLYMETALLIC BIOLEACHING AT FLASK LEVEL

“…Mimetite (Pb 5 (AsO 4 ) 3 Cl) and hemimorphite (Zn 4 (Si 2 O 7 ) (OH) 2 •H 2 O) can be dissolved by protonation. Turek et al (2015) observed in mimetite five and 11 times more As and Pb dissolved at pH of 2.5 compared to 3. 75, respectively.…”

Potentially Harmful Elements (As, Sb, Cd, Pb) in Soil Polluted by Historical Smelting Operation in the Upper Silesian Area (Southern Poland)

“…This mineral is most often formed in the final stages of the transformation of Pb arsenates [45], commonly described as a secondary mineral in the oxidation zone of Pb-As deposits [46,47] and in the weathering of slags [48]. Arsenic and Pb minerals are relatively numerous but, in nature, are rare [49]. It is a relatively insoluble and thermodynamically stable mineral, particularly at a pH > 5 [50].…”