A review of chemical, electrochemical and biological methods for aqueous Cr(VI) reduction

Hexavalent chromium is of particular environmental concern due to its toxicity and mobility and is challenging to remove from industrial wastewater. It is a strong oxidizing agent that is carcinogenic and mutagenic and diffuses quickly through soil and aquatic environments. It does not form insoluble compounds in aqueous solutions, so separation by precipitation is not feasible. While Cr(VI) oxyanions are very mobile and toxic in the environment, Cr(III) cations are not. Like many metal cations, Cr(III) forms insoluble precipitates. Thus, reducing Cr(VI) to Cr(III) simplifies its removal from effluent and also reduces its toxicity and mobility. In this review, we describe the environmental implications of Cr(VI) presence in aqueous solutions, the chemical species that could be present and then we describe the technologies available to efficiently reduce hexavalent chromium.