Application of waste acid from phosphogysum dam as an eco-friendly depressant in collophane flotation

Abstract Dealing with waste acid generated in phosphoric acid (H3PO4) production has always been a problem due to the lack of cost-effective and environment-friendly disposal technology. This study introduces a novel method of utilizing the waste acid as a depressant in collophane flotation aiming at reusing waste acid and reducing the consumption of sulfuric acid (H2SO4) in flotation plants. Its effectiveness was confirmed by flotation test in lab- and industrial-scale test. The depression mechanism is investigated via solution chemistry calculation and scanning electron microscope analysis. Laboratory-scale flotation results indicate that the utilization of waste acid coupled with H2SO4 can strengthen depression performance on collophane, improving recovery efficiency compared with the use of H2SO4 alone as depressant. Results demonstrate that H2PO4− is the effective species in waste acid. It depresses the flotation of collophane by reacting with active Ca sites on the surface to form CaHPO4 and Ca(H2PO4)2, thus preventing collector adsorption and reducing collophane surface hydrophobicity. The application of waste acid in industrial test shows the flotation recovery increases by 1% accompanied with the reduced consumption of H2SO4 by 30.03% (from 15.5 kg/t to 10.8 kg/t). An increased profit of 890,043 RMB in a month is achieved due to the application of waste acid. Notably, approximately 197,000 t waste acid is consumed for a month, which brings considerable environmental benefits. In summary, the application of waste acid in collophane flotation is an efficient, economical, and eco-friendly alternative for the treatment of waste acid.