Fundamental Electrochemical Behavior of Antimony in Alkaline Solution

Abstract

Even though electroplating has been applied to extract antimony from the relevant mines, such as stibnite (Sb2S3) and valentinite (Sb2O3), there are still some unclear points which need to be clarified: in alkaline sulfide solution, S2− can help increase the solubility of Sb(III) ions. In the present study, cyclic voltammetry (CV) and chronoamperometry (CA) tests were employed to investigate the electrochemical behavior of antimony ions in KOH solution (20 wt%), and the results revealed that Sb(III) ions have much higher electrochemical activity than Sb(V) ions. However, Sb(V) ions are not completely inactive at the potential before H2 evolution reaction, as previous studies reported, and part of Sb(V) ions can be electroplated in the KOH solution. The contradictions between the present and previous studies are due to the impurity caused by Sb(III) ions, which are speculated to play a role in Sb(V) ion reduction. Ions such as As3+, Si4+, CO32−, Al3+, and Sn2+ show no interference on the electroplating of antimony. Other electrochemical and chemical behaviors are clarified in this study as well: (1) the Sb(III)/Sb(0) couple is more electrochemically reversible at the interface of antimony metal/KOH solution than that at the interface of a glass carbon/KOH solution; (2) in a sulfide alkaline solution system, S2− ions can coordinate with Sb(III) ions and lower the reduction potential of Sb(III) ions to antimony metal, thus leading to a lower current efficiency of antimony electroplating. The reducing reagents, including KI, K2SO3, and KBH4, can reduce Sb(V) ions to Sb(III) ions in an acid solution, but these chemical reduction reactions cannot happen in the KOH solution. These fundamental studies can provide knowledge on antimony refining from the relevant secondary resources.