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A step closer to producing waste-free, green alumina

Tests reveal positive leaching results for aluminium and calcium from anorthosite, pointing to the rock as a key solution to sustainable aluminium production.

Industrial Technologies

Canadian mineral exploration company Hudson Resources recently announced the results of tests carried out on anorthosite, an igneous rock found in Greenland’s White Mountain mine. Conducted by the Institute for Energy Technology (IFE), Norway, as part of the EU-funded AlSiCal project, the tests confirm that the anorthosite yields very high leach recoveries with short leaching times when aluminium and calcium are dissolved. As Hudson Resources reports in a press release posted on ‘GlobeNewswire’, “this is the key first step in the production of a waste-free smelter grade ‘Green Alumina’ product for the aluminum industry.” The company aims to provide evidence of an economic process for producing such a product from anorthosite. The anorthosite samples provided for testing included a -250 μm product and coarse (+100 mm) rock samples that were crushed and sieved down to 77-760 μm. After testing the high-quality samples, AlSiCal project coordinator IFE found that both aluminium and calcium were leached simultaneously and that 87-97 % wt% (weight per cent) of leaching occurred in the first 2 hours. The tests also revealed 93-100 % wt% leaching took 4 hours and that the variability within range is due to varying particle sizes and/or the natural heterogeneity of anorthosite. According to the IFE, the samples demonstrated “fast leaching” characteristics and a “high total dissolution yield (being 100% the theoretical, calculated maximum dissolution yield based on the available analyses).”

The leaching process

The leaching tests the IFE carried out comprised the following steps. Anorthosite was mixed with 20 wt% hydrochloric acid at 140 ℃. The final reaction mixture was then cooled, following which liquid and solid fractions were separated using a centrifuge and decanting. The solid fractions were washed and dried. “The EU funded testwork conducted by IFE and AlSiCal independently confirms an efficient and straightforward leaching process of aluminum and calcium from the White Mountain anorthosite,” observed Hudson Resources President Jim Cambon. “This represents a key step in the production of a waste-free ‘Green Alumina’ product and offers a direct replacement to bauxite which creates almost four tonnes of waste for every tonne of aluminum produced. The time is right for the production of a truly green aluminum in which anorthosite is a key solution.” The AlSiCal (Towards sustainable mineral and metal industry: ZERO Bauxite Residue and ZERO CO2 from co-production of Alumina, Silica and precipitated Calcium carbonate by the Aranda-Mastin technology) project aspires to make the mineral and metal industry more sustainable and environmentally sound. To this end, it’s developing an innovative technology that will make it possible to co-produce alumina, silica and precipitated calcium carbonate without generating any bauxite residue or CO2 emissions. This feat will be made possible through the use of abundantly available resources such as anorthosite. For more information, please see: AlSiCal project website

Keywords

AlSiCal, alumina, anorthosite, leaching, calcium, aluminium, mineral, bauxite