Sustainable Metal Recovery from Secondary Resources: Screening and Kinetic Studies Using Analogue Heterotrophic Metabolites

Abstract

This study presents a sustainable approach for metal extraction from a range of secondary resources. Organic acids analogue to those commonly produced by heterotrophic microbes are applied via a two-step heterotrophic bioleaching approach. New insights into leaching mechanisms are developed and the potential use of the leaching residues as cementitious component is evaluated. Tested materials include a jarosite sludge from Zn refining, four ferrous metallurgy residue sludges and two dry automotive recycling shredder residues. Screening experiments tested three organic acids (i.e. citric, gluconic, oxalic acid) and their combinations. Four physicochemical factors were varied, i.e. the solid/liquid ratio between 5 and 15%, total organic acid concentration between 20 and 200 mM, leaching times of 2 to 4 h and horizontal stirring reactor mixing rate. The highest extraction capacity was achieved for a Cr/Ni rich sludges from steel treatment with up to 96% Ni and 91% Cr extraction at a 5% S/L and a mixture of 100 mM citric and 100 mM oxalic acid. Further scale-up kinetic studies on this Cr/Ni sludge validated the optimal leaching conditions. Modelling of kinetic leaching data indicated pore diffusion rate as a bottleneck of the overall leaching process. Screening tests of the leached residue indicated potential use as sulfate-rich addition to cement, or as part of low-performance binders for large scale civil works.