Abstract
There is considerable interest in the development of new processes to extract the nickel from the oxidic nickeliferous laterite deposits, as the global nickel sulphide resources are rapidly becoming more difficult to access. In comparison to sulphide ores, where the nickel-containing mineral can be readily concentrated by flotation, nickel laterites are not amenable to significant upgrading, due to their complex mineralogy. In this paper, firstly, a brief overview of the conventional techniques used to process the nickeliferous limonitic laterites is given, as well as a review of current research in the area. Secondly, a thermodynamic model is developed to simulate the roasting process and to aid in the selection of process parameters to maximize the nickel recovery and grade and also to minimize the magnetite content of the concentrate. Thirdly, a two-stage process involving reduction roasting and thermal growth in either a tube furnace or a rotary kiln furnace, followed by magnetic separation, was investigated. Thermogravimetric, differential thermal and mineral liberation analyses techniques were utilized to further understand the process. Finally, the nickel grades and recovery results were compared to those available in the literature.
Highlights
Nickel metal is primarily employed in high nickel alloys and superalloys
There are three commercial processing routes for nickel laterite ores as shown in Figure 1 and the method selected depends on the ore composition
On cooling the reduced limonite from 800 to 25 ◦ C in air, there were no evident changes in the phases, suggesting the stability of the phases formed at higher temperatures
Summary
Nickel metal is primarily employed in high nickel alloys and superalloys. Nickel utilization is increasing at a rate of about 4% per year [1]. The upper limonitic layer of the deposit consists of mainly goethite ((Fe,Ni)O·OH) with some hematite (Fe2 O3 ) and some magnesium silicates These ores contain substantial amounts of water, and the nickel has traditionally been extracted via hydrometallurgical processes. Minerals 2017, 7, 176 successful recovery of the nickel and potentially the cobalt would be to selectively reduce all the nickel and cobalt oxides and some of the iron oxide via low temperature solid state reduction to produce an intermediate product, known as ferronickel This reduced product could be further upgraded downstream, by removing the unreduced oxides, so as to produce a concentrate, and magnetic separation could be considered as a suitable method for concentration. Thermogravimetric, differential thermal and mineral liberation analyses techniques were utilized to further understand the reduction process
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