Evaluation of hydrazine, dimethylamine borane and glyoxylic acid as reducing agents in reductive precipitation.

The mechanisms of heavy metal removal (Fe, Al and Mn) from acidic mineral effluents (pH <3) by reductive precipitation using basic oxygen furnace slag (BOFS) as a seeding agent was studied. The mechanisms of removal were determined using spectroscopic techniques (FTIR, XRD and XRF) to study the microstructural and composition changes of the seeding material. It was established that the sorption process occurred predominantly by chemisorption for trivalent cations i.e. Al³⁺ and Fe³⁺, while for divalent cations i.e. Mn²⁺ removal occurred through ion exchange and chemisorption. Furthermore, the results showed that the incorporation of metal ions in the BOFS structure caused chemical changes in the FTIR spectra. The results showed that the removal of metal ions from effluents using hydrazine as a reducing agent was thermodynamically feasible with the following removals: 99.9% for Fe (III) and Mn (II), 99% Al (III) using synthetic solutions. The% removals of Fe (III) and Mn (II), Al (III) using DMAB as a reducing agent were not significantly different from those obtained using hydrazine. Metal removal using glyoxylic acid as a reducing agent was not thermodynamically feasible; hence the% metal removals were the lowest i.e. Al (85%), Fe (97.5%) and Mn (94%) compared to hydrazine and DMAB.