The flotation behavior and adsorption mechanism of a-hydroxyoctyl phosphinic acid (HPA) to malachite were investigated by micro-flotation tests, zeta potential measurements, and FTIR and XPS analysis. The micro-flotation results demonstrated that compared with sodium isobutyl xanthate (SIBX) and styrene phosphonic acid (SPA), HPA exhibited superior collecting performances to direct flotation recovery of malachite and floated out above 80% malachite at pH 5-10. The results of zeta potential measurement inferred that there might be covalent bonds between HPA and copper on the malachite surface. The FTIR analysis confirm that HPA might react with copper species of malachite surfaces to form Cu-HPA complex adsorption layers, with a release of H ions (from P-H group). The XPS analysis provided very clear evidence that the Cu(II) species was partly reduced to Cu (I) species during HPA chemisorption on malachite surfaces, accompanying P(III) oxidation to P(V) species of HPA. (C) 2014 Elsevier Ltd. All rights reserved.