High-Efficiency Enrichment of Precious Metals with Mechanochemically Enhanced Galvanic and Kirkendall Effects

We report mechanochemical enrichment of metals (e.g., Ag(I), Au(III)) by harnessing microscopic galvanic and Kirkendall effects. Experimental results show the mechanochemical reactions can directly produce high-purity precious metals (e.g., 78.9% Ag and 68.6% Au, respectively) from wastewaters. One mole of zerovalent iron (ZVI) can harvest up to 2.18 mol of Au or 3.74 mol of Ag from wastewaters, respectively, which stand for 900% and 2291% enhancement above the results from conventional solution chemistry. The mechanochemical reactions foster highly favorable conditions for metal cation sequestration (alkaline pH, negatively charged nanoparticles, and low redox potential). Together with the continuous surface renewal, mechanochemical energy manifests an extraordinary efficiency for metal enrichment. Laboratory experiments further demonstrated that it performed equally well on other metal ions (e.g., Pd(II), Cu(II), Ni(II), Pb(II), and Co(II)), suggesting its potential as a versatile solution for metal enrichment and recycling.