Major Environmental Benefits Recycling Gold with Biodiesel

(Chalmers University of Technology/EurekAlert!) ... In the researchers' method, gold scrap − usually in the form of small earrings that Mark Foreman buys at his local pawn shop − is dissolved in a mixture of hydrochloric acid and nitric acid (aqua regia). The gold found in jewellery is an alloy with other metals, including silver, and this leads to the silver depositing in solid form as silver chloride. In just two more steps, pure gold is then extracted from the solution. Firstly, HVO100 and the chemical malonamide are added, and secondly the entire mixture is shaken with ordinary salt water. The method used by the Chalmers researchers is even more ‘green’, since the malanomide was made from renewable biomass, which replaces more toxic and carcinogenic chemicals that are traditionally used to purify gold scrap.

"Our method is an environmentally friendly way of extracting pure gold from a mixture of many metals. Similar studies have been carried out in the past but have not achieved such a high purity of gold. The combination of biodiesel and malanomide is also special because it replaces both fossil diesel and other problematic chemicals. HVO100 is also very clean and works great in a laboratory, you don't need to make a special order, you just have to go to the nearest station and refill your canister," says Mark Foreman.

Normally, when metals are mined or recycled, large amounts of fossil solvents are needed, but this doesn’t have to be the case, and the method developed by Chalmers researchers can be used for more metals than just gold. An important example is copper, a metal that is very common as a conductor in electronic components. In 2022 alone, more than 26 million tonnes of copper was used in the world, and according to the analysis company GlobalData, there are more than 695 active copper mines globally. About 75 percent of the world's copper mines use fossil solvents to purify the metal, and depending on the size, a mine needs up to 1,000 tonnes of solvent to purify the copper mined there. Solvents that could be replaced by biodiesel.

The same method can be used to purify and recycle many other socially important metals, such as platinum, which is used in catalysts; nickel and cobalt in batteries; uranium and plutonium for the nuclear industry; and rare earth elements. The latter are a prerequisite for the rapid development of everyday electronics such as smartphones and tablets, and are important for modern green technology, such as in wind turbines and electric vehicles. READ MORE

Excerpt from RSC Sustainability: This paper presents the basis for an industrial gold purification process using an organic phase made from biomass derived organic chemicals is presented. The use of a sustainable kerosene (a biodiesel) as a diluent in a solvent extraction experiment is important as it allows the solvent extraction of metals to be done without petroleum kerosene. A chemical change in the organic phase which reduces the gold distribution ratio has been observed and rationalized with XANES/EXAFS, this change offers path towards more sustainable flowsheets for gold. A second process is also presented using biomass derived diluent, the parameters required to calculate the ratio of the activity functions of chloride and the tetrachloroaurate(III) complex in choline chloride media are within this paper. Additionally solvent extraction experiments using the new sustainable diluent for lithium and alkaline earth elements together with proof of principle experiments with stable lanthanides, 99mTc, 152Eu, 238Pu and 239Pu were performed. READ MORE