Minerals processing is going organic

It all started with a company that would not take no for an answer.  
Resource Mining Corporation (RMC) had held its key project the Wowo Gap for some time.  
Hosting nickel and cobalt, in the words of the company it is "a large resource, lies close to the surface, and is of high quality".  
It has an indicated and inferred resource estimate of 125 million tonnes at 1.06 per cent nickel and .07 per cent cobalt.  
However RMC faced a small problem.  
This Papua New Guinean project is two thirds saprolite and only one third limonite.  
So in actually processing its nickel and cobalt in the traditional method – using sulphuric acid – it was in danger of losing much of its minerals.  
Resource Mining managing director Warwick Davies told Australian Mining it needed a better way to process.  
"If we used conventional sulphuric acid we found it just digested the magnesia in the saprolite," Davies said.  
RMC need a solution, so it developed its own by using an organic acid that is able to digest the other minerals to allow the miner access to more of the nickel and cobalt, without sacrificing it as would have been the case with sulphuric ­acids.  
"This development is ­really a positive for nickel laterites," Davies told ­Australian Mining.
"What really drove this development," Davies said, "is that while carrying out feasibility studies with sulphuric acid we found that the project would become uneconomical; we essentially had a resource that we couldn't process with conventional technology.  
"So instead of abandoning such a prospective project, we went off and investigated other processes; knowing that there are hundreds of acids we knew that there would be the potential to do this job with another organic acid, and eventually found one."  
He explained that this was new territory as the use of sulphuric acids in the digestions of nickel laterites has typically been the process of choice, as sulphuric acid was cheap, readily available, and it had simply been the way it was always done in Australia.  
The study into using this organic acid leach really kicked off in December last year following a $250 000 grant from Commercialisation Australia to provide the proof of concept for its organic acid nickel recovery process.  
At the time Davies said "the organic leaching pro­cess provides a more cost effective alternative to a standard high pressure acid leach process and this grant is especially important because it has the potential to change the project economics from a development perspective and be better for the environment".  
He told Australian Mining that this technology has since demonstrated its ability to be used on limonite and saprolite ores.  
"Now we are working towards optimising its efficiency."  
Recent test works have shown it can achieve 98 per cent nickel extraction from saprolite materials after less than half an hour.  
Test work on the limonite materials has confirmed leach extractions of up to 80 per cent after 90 minutes.  
"We are now optimising conditions, looking at different acid strengths, conditions, and time," Davies said.  
Resource Mining is also looking at extracting the dissolved nickel and cobalt from the solution as well as acid regeneration and leaching kinetics.  
Aside from the immediate value to Resource Mining, Davies explained that processing nickel laterites using this organic acid will make a number of previously uneconomic deposits viable, not just to process but also for capital costs.  
"What this does is not only make deposits more economical, but also provides scalability in processing because with this organic acid you don't need high tech equipment or requirements – you can use poly pipe instead of stainless steel tanks and piping, so you can have a much smaller plant size which means that your capital costs will be lower," Davies explained.  
"This changes the dynamics as the processing operations is scalable downwards.  
"Importantly it also has the potential to process lower grade nickel deposits; however we don't see this organic process really changing the nickel price."  
Resource Mining Corporation has engaged the CSIRO, under a Consulting Services Agreement, to aid the miner in scoping and mass balancing of the leach tests under a variety of conditions; test optimisation; and acid purification and recovery.  
The initial contract with the CSIRO is for a six month period.
Image: Kimopax

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