Roasting and Leaching Behavior of Nickel Laterite Ore

Nickel is mostly extracted from sulfide ores, however, laterite ores account for over 60 pct of all nickel resources in the world, and despite its predominance, there is no well-established process to extract nickel from such ores. Nickel in laterites is hosted in many different compounds such as oxides, hydroxides, and silicates minerals. The sulfation-roasting-leaching process has the potential to change this scenario once it can be applied to all kinds of nickel laterite ores and does not consume much acid, as in the atmospheric leaching process. The main characteristic of the process is the iron sulfates decomposition during roasting steps, which produces sulfur trioxide (SO3). The sulfur trioxide is reactive with metals such as nickel and cobalt, converting them to soluble sulfates, and reducing acid consumption. Experiments were conducted to establish the optimal conditions to extract nickel from laterite ores using the sulfation-roasting-leaching process. Various parameters were investigated: water addition, sulfuric acid concentration, the number of heat-treatments steps, roasting temperature and time, leaching time, and solid/liquid ratio. Furthermore, the phase changes during thermal treatments were investigated to identify the mechanisms involved in the transformation of the minerals. Experimental results indicated that nickel forms sulfates through three different ways: reacting with H2SO4 during sulfation, with Fe-2(SO4)(3) (ferric sulfate) or Fe(OH)SO4 (basic iron sulfates) during the heat-treatments, and also throughout the leaching step due to iron-rich phase dissolution. More than 83.0 pct Ni, 90.0 pct Co, 61.3 pct Al, 17.3 pct Ca, 85.7 pct Mg, 87.5 pct Mn, 1.1 pct Ti, and 16.6 pct Fe were extracted under optimums conditions. [GRAPHICS] .