| Description |
Nickel laterites are becoming more attractive for nickel production due to the depletion of high grade nickel sulfide ores. Since the nickel content in laterites is relatively low, processes to recover nickel from these resources must be economical and robust. Heap leaching has been commonly used to treat low grade copper and gold ores due to its low capital and operating costs. Therefore, research and development in nickel heap leaching technology is compelling. However, nickel laterites typically contain significant quantities of fine particles and clay minerals which could contribute to heap leaching difficulties. Agglomeration has been used to improve heap performance in copper and gold heap leaching. Experiments have been conducted to evaluate the performance of agglomeration in nickel heap leaching. In this study, nickel laterite ores were agglomerated with various conditions, including moisture content, acid concentration, retention time and drum rotation speed. Size distribution, permeability and electrical conductivity data of agglomerates were collected to study the effects of agglomeration conditions on agglomerate qualities. The agglomerates were then leached with diluted sulfuric acid for 90 days. Nickel and other interested element extraction rates were obtained by ICP-OES. Mineralogy of feeds, agglomerates and leached residuals were also investigated. From the experimental data, we found that agglomerate size distributions (ASD) correlated with the agglomeration volume of solution added agglomeration. The drum rotation speeds did not a have significant effect on agglomerate size distribution. Increasing mixing times during agglomeration led to increases in agglomerate sizes. Hydraulic conductivity (permeability) of the agglomerate bed is related to the agglomerate size distribution. The electrical conductivity of nickel laterite agglomerate beds depends on the sulfuric acid concentration used during agglomeration, solution addition, external compression and nature of the ores. Nonetheless, the values depend heavily on the sulfuric acid concentration. The highest extraction rate of nickel, cobalt, iron, aluminum, magnesium and manganese in these experiments are 58%, 38%, 22%, 28%, 48% and 27%, respectively. The feed contains mainly silico-ferruginous plasma, goethite and clay minerals along with other minor phases. In agglomerates, a new sulfate phase was observed. The main element in this phase is sulfur. The "sulfate" phase and clays appear to dissolve during leaching. The nickel that remained unleached predominantly resides in the silicoferruginous plasma. |
