Pieter Ostermeyer

Over the past decades, biological treatment of metallurgical wastewaters has become commonplace. Passive systems require intensive land use due to their slow treatment rates, do not recover embedded resources and are poorly controllable. Active systems however require the addition of chemicals, increasing operational costs and possibly negatively affecting safety and the environment. Electrification of biological systems can reduce the use of chemicals, operational costs, surface footprint and environmental impact when compared to passive and active technologies whilst increasing the recovery of resources and the extraction of products. Electrification of low rate applications has resulted in the development of bioelectrochemical systems (BES), but electrification of high rate systems has been lagging behind due to the limited mass transfer, electron transfer and biomass density in BES. We postulate that for high rate applications, the electrification of bioreactors, for example, through the use of electrolyzers, may herald a new generation of electrified biological systems (EBS). In this review, we evaluate the latest trends in the field of biometallurgical and microbial-electrochemical wastewater treatment and discuss the advantages and challenges of these existing treatment technologies. We advocate for future research to focus on the development of electrified bioreactors, exploring the boundaries and limitations of these systems, and their validity upon treating industrial wastewaters.

The treatment and hydrometallurgical recovery of Pb from zinc leaching residue (ZLR), a waste stream generated by the zinc refining process, is proposed in this work. Leaching achieved complete extraction of Pb (140 mg/g) within 24 h contact time using a 0.8 M sodium citrate solution. The batch leaching process that operates at ambient temperature results in a pregnant leachate solution of dissolved lead citrate. Pb is recovered from the dissolved organometal complex as a precipitate of PbSO4 after chemical reaction in acidic conditions that are maintained through continuous membrane electrolysis. In addition, an alkaline buffer is generated at the cell cathode to regenerate the leachate, so that the recycled lixiviant can be used in consequent leaching steps. Characterization of the final product by XRD, ICP-AES, and Raman spectroscopy identified an amorphous PbSO4 phase with traces of lead citrate. The overall purity of Pb is 46 ± 4%, representing a 3.3 fold concentration of ZLR. The integrated process is capable to treat ZLR sustainably. It can resolve the need for landfilling the mineral tailing and treat historic dump sites, respecting the zero-waste rationale, while also recovering raw material from a secondary source.

Copper producers face increased demand associated with increasing complexity in feedstock composition, including high amounts of impurity metals. In this work, linear sweep voltammetry was used to study the electrodeposition behavior of copper and arsenic, define strategies for the production of grade A copper, and the removal of arsenic from complex electrolytes. Our results show that the copper concentration is a key parameter to control in the electrodeposition process. The continuous deposition of arsenic from the electrolyte requires copper in solution ( ≤ 10 g L-1 Cu(II) for 2 g L-1 As(III)) to form copper arsenides. The deposition of metallic arsenic does not occur readily. Conversely, the use of a concentrated Cu(II) solution (e.g. 40 g L-1) resulted in grade A copper from an electrolyte with a maximum of 2 g L-1 As(III) under galvanostatic control at a current density of - 42 mA cm-2. Time-of-Flight Secondary Ion Mass Spectrometry depth profile measurements on copper deposits revealed that arsenic contamination was entirely concentrated near the substrate side of the deposit and progressively decreased further into the deposit. The codeposition of arsenic occurred along with the initial copper nucleation, when the electrochemical potential for electrodepostion under galvanostatic control is temporarily lower. These findings provide important insights for future sustainable copper electrodeposition technologies from complex feedstocks

Precipitation of arsenic as As2S3 produces little waste sludge, has the potential for low chemical consumption and for selective metal(loid) removal. In this study, arsenic removal from acidic (pH 2), metallurgical wastewater was tested in industrially relevant conditions. Sulfides added at a S:As molar ratio of 2.5 and 5 resulted in removal of 99% and 84% of As(III) and As(V). Precipitation of As2S3 from the As(III) and industrial wastewater containing 17% As(V) was nearly instantaneous. For the synthetic As(V) solution, reduction to As(III) was the rate limiting step. At a S:As ratio of 20 and an observed removal rate (k2 = 4.8 (mol L-1) h-1), two hours were required to remove of 93% of arsenic from a 1 g As L-1 solution. In the case of As(V) in industrial samples this time lag was not observed, showing that components in the industrial wastewater affected the removal and reduction of arsenate. Speciation also affected flocculation and coagulation characteristics of As2S3 particles: As(V) reduction resulted in poor coagulation and flocculation. Selective precipitation of arsenic was possible, but depended on speciation, S:As ratio and other metals present.