Flame-retardants utilising antimony are often incorporated into polymers (plastics) destined for safety equipment, household goods, electronics and aerospace components. Antimony also imparts properties like strength, hardness and corrosion resistance to alloys used for industrial applications including lead-acid storage batteries, pipes and ball bearings. Antimony is primarily obtained from mining ores (rocks and sediment containing antimony together with minerals or metals). Most of the world’s antimony comes from China, and European companies require an alternative solution. EU-funded researchers working on the Stibiox project have developed patented eco-friendly process technology to easily recover antimony from a variety of sources. Its utility does not end there. Along with antimony, the process results in separation and isolation of the other metals with which it is bound, yielding additional marketable compounds.
More profit with lower environmental impact
According to project coordinator Christian Thomas, “It is currently quite difficult to separate antimony, arsenic, tin and lead. The existing processes are expensive and hazardous.” Stibiox has made that process safe, less expensive and more effective. Antimony mining companies that face difficulties extracting antimony from high-lead ores could soon have an easy and inexpensive way to get the job done. The lead industry adds antimony to improve properties of metal components. Currently, companies sell excess antimony at a low price due to high impurity. Stibiox technology may help them increase their profits. Antimony trioxide is commonly used with brominated flame retardants to significantly increase their effectiveness. The flame retardant is added as pellets known as ‘masterbatch’ to polymeric compounds during production. As Thomas explains, “Brominated plastics must be separated and incinerated. The ashes have a significant content of antimony which is currently not recovered.”
Four steps in an eco-friendly process yield four distinct metal oxides
According to Thomas, “In the first step of the Stibiox process, thermal oxidation produces oxides of all the metals present. Sulfuric acid leaching then takes out antimony, tin and arsenic in solution and leaves lead in the solid fraction. Solvent extraction allows separation of antimony, tin and arsenic. Desorption in the fourth and final step yields the oxide of each of the four metals in a marketable quality.” Recycling all the reagents significantly reduces process costs. In addition, it limits disposal of reaction solutions, tremendously enhancing environmental and personal safety. Overcoming the hazards of metallurgy is one of the outcomes of which Thomas is most proud. As he explains, “There is no risk of producing highly toxic gases such as stibine or arsine. There is no risk linked to molten soda manipulation which has been deadly in the past. There is no final waste. Our engineers, with extensive experience in the metallurgy of non-ferrous metals, worked long and hard to solve these issues – and we finally did it!”
On the road to industrialisation
Thomas and his team are developing a pilot plant to process antimony from various sources in large quantities. The next step is planned construction of an industrial plant capable of producing 5 000 tonnes of antimony per year. From there, the project’s impact is likely to be felt up and downstream of the antimony recovery process – but thankfully not in the environment.
Stibiox, antimony, metals, lead, eco-friendly, process technology, metallurgy, separation, mining, ores, brominated, polymer, plastics, pellets, masterbatch, recycling, flame-retardant