Cost-effective use of duplex stainless steel for structural application in hydrometallurgical processes for the production of lithium and battery metal materials

The production of lithium ion batteries involves materials produced by hydrometallurgical processing of primary or secondary resources of lithium, nickel, cobalt, copper and manganese. These processes typically involve highly corrosive conditions due to the use of reagents such as sulphuric acid, chlorides, and in some cases high temperatures and pressures, so that the optimum selection of materials of construction for items such as pressure vessels, thickeners, process tanks, and other process items is a key issue. Stainless steels of type 304 or 316 are often considered as too expensive to be used as a multipurpose construction material with a price level several times higher than carbon steel. Therefore, they are only selected when it is absolutely necessary in harsh environments. Additionally, their mechanical strength is relatively low, similar to mild steel, which limits structural efficiency. Furthermore, stainless steel can also corrode if wrongly selected, they are not immune, and the way they corrode are often more unpredictable compared to carbon steel. Thus, why even consider using stainless steel as an alternative to coated carbon steel for structural applications? There are several different types of stainless steel on the market where the austenitic type 304 and 316 are the most commonly used, however, this paper elaborates on how duplex (two-phase, austenitic-ferritic) stainless steel can provide cost-effective solutions for structural applications typically used in the hydrometallurgical processes used to produce materials for battery production. The severe conditions set a great demand on which material to select to entirely avoid corrosion. Moreover, the presence of metallic ions also has an inhibiting effect on the onset of corrosion in these environments. To assist in such complex material selection cases, there are several tools available for the designer, e.g., laboratory test data and field experience, to indicate the proper alloy which can resist corrosion but not to provide an over-specified solution. However, the best practice to pinpoint a suitable material with higher confidence for complex cases is often to carry-out a field test using a test-rack with steel samples of different rank to be exposed to the specific intended environment. duplex stainless steels can often provide a more cost-effective solution, by utilizing their high mechanical strength together with adequate corrosion resistance and without the need for expensive protective coatings. The cost of coating a carbon steel can easily be in the same range as the alloy cost, especially if repair, maintenance and lost production cost are considered as well, and the total life cycle cost is emphasized, not only the initial investment cost. A case study for the latter using an in-house developed whole cost calculation tool will illustrate possible cost advantages of using duplex stainless steel for tank applications. Finally, this paper will outline references cases which showcase metallurgical processing related applications where duplex stainless steels have been selected world-wide including a Lithium plant in Western Australia. (author)