The world may have an excess of nickel ore these days, but that has not always been the case in the past and certainly will not be in the future.
There is a great deal of uncertainty around the current low prices’ potential impact on NPI in China and on Indonesia’s move to increase refining value add operations rather than allow the export of basic concentrate. But as sulfide ore grades decline, it’ll be an inevitable transition from exploiting currently dominant sulfide deposits, such as Ontario’s Sudbury resource, to the more widely available laterite nickel ore deposits.
The British Geological Survey estimates that 73% of the continental world nickel resources are lateritic, yet the currently dominant extraction process – High Pressure Acid Leach (HPAL) – is technologically challenging and costly. So when a new technology approaching commercial application claims to incur production costs of less than half of HPAL’s sulphuric acid leach, it raises the prospect of opening up many new sources of supply currently considered uneconomic.
Pyrometallurgy and acid leach
There are two principle methods of exploiting laterite deposits. Pyrometallurgy produces the ferronickel or nickel pig iron used in stainless steel making, and matte (a mixture of copper and nickel), which is further refined in downstream smelting processes. The other is acid leach, with HPAL being the most popular subtype. To achieve economic recovery from the ore, conventional sulphuric acid leaching requires temperatures above 230 degrees C and atmospheric pressure up to 44 atmospheres.
Consequently, modern HPAL requires titanium-lined autoclaves and sulphuric acid generation, and the demanding nature of the process has led to cost overruns and delays on HPAL projects in recent years. But a new process using hydrochloric acid in place of sulphuric acid is reaching a successful 19 stage campaign of trials and tests prior to commercial investment. Direct Nickel (DNi) in Australia has worked with CSIRO and other partners to test the technology at their plants in Perth. Readers of this site will have heard us credit CSIRO with technological advancements before. They’re a good example of state-funded scientific research supporting commercial endeavor.
Why use nitric acid?
The use of nitric acid has several advantages over the current sulphuric acid HPAL technology. First, it can treat different kinds of laterite ores in the same process circuit, and second, recycling of the nitric acid allows for very low total acid consumption, thus reducing costs. The process takes place at low atmospheric pressure and temperatures of only 100 degrees C, allowing the use of cheaper stainless steel containment vessels. At just 2-4 hours for leaching, the process is faster, and the resulting waste is much less than HPAL in volume (by half, according to most estimates). And the waste is formed from silicates on which plant matter will grow, rather than the sulphide residues that makes up HPAL waste.
Environmental factors aside, it is the economics that will promote an early adoption of the DNi process, holding out the prospect of widening the resource base and lowering production costs for struggling nickel producers. One caveat is that mining companies and refiners will find it tough to raise significant capital in today’s over-supplied nickel market. However, an existing HPAL plant may look to transition across to the new technology if they are convinced the pay back was fast enough. In the longer term though, DNi appears to have much to be commended for, and we look forward to hearing of DNi’s first full-scale plant commissioning.