Recovery of heavy metal ions and recycle of removal agent in the polymer–surfactant aggregate process

Abstract

Abstract In a previous work, a novel effluent treatment process was developed and applied to remove heavy metal ions from dilute aqueous solutions using polymer–surfactant aggregates (PSAs) (Shen et al., 2015). A subsequent pH adjustment method for the polymer–surfactant aggregate process has been developed to recover the heavy metal ions from the flocculated PSAs into a concentrated solution and to regenerate the PSAs for recycle. The PSA is a colloidal structure that is formed by micelle-like aggregates associating with the oppositely charged polymer chains. The PSA can then bind with heavy metal ions and precipitate out of the solution. In the work presented, the flocs are firstly acidified using a small volume of 0.05 M H2SO4. The bound metal ion are leached out in 15 min, and pass through a coarse filter to report as a metallic ions solution 20–50 times more concentrated than the original effluent. After the acid leaching, the flocs can be completely dissolved in a small volume of 0.1 M NaOH. This basic polymer and surfactant solution is then reused in the next treatment cycle; meanwhile, the pH of the solution is neutralised by adding H2SO4. The results show that the removal efficiency of 11.2 ppm Cd(II) solution remains above 97% after 5 cycles without the need for make-up of the removal agent. The recovery efficiencies of Cd(II), Zn(II), and Cr(III) remain above 91%, 86% and 73%, respectively, after 6 cycles. In addition, a MATLAB simulation shows that the accumulations of Na2SO4 are stabilised at 280 ppm after the third cycle. Thus, the pH adjustment method is able to recover and concentrate the metal ions from the flocculated PSAs, and also to regenerate the removal agent such that it can be recycled with little deterioration of removal ability.