Column leaching of low-grade saprolitic laterites and valorization of leaching residues

Research paperSummarization: Socio-economic data on nickel and cobalt show their importance throughout the entire metal value chain, from mining to end use, disposal and recycling. Thus, the extraction of both metals from primary and secondary raw materials as well as from wastes is currently considered strategically important for the industry and the society. In this paper heap leaching of Greek low-grade saprolitic laterites, with Ni content 0.97%, was investigated. The main parameters studied involved the strength of the H2SO4 solution used (49 and 147 g L−1) and the effect of adding sodium sulfite (Na2SO3) in the leaching medium. The pregnant leach solution (PLS) was recycled several times during leaching in order to minimize acid consumption. The experimental results showed that within a period of 25 days, and under the optimum conditions (147 g L−1 H2SO4 and 20 g L−1 Na2SO3), i) Ni and Co extractions were 72.5% and 47.4%, respectively and ii) Fe and Al co-extractions were 8.7% and 31.3%, respectively. Furthermore, valorization of the leaching residues through alkali activation using NaOH and Na2SiO3 and the addition ofmetakaolin (MK) for the production of inorganic polymers (IPs)was explored. X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transforminfrared (FTIR) spectroscopy, Differential scanning calorimetry (DSC/ TG) and Scanning electron microscopy (SEM-EDS)were used to characterize the ore, its leaching residues and the IPs. The IPs produced demonstrated high compressive strength, almost 40MPa and are suitable for a wide range of applications in the construction sector.Presented on: Science of the Total Environmen