Metal ion/metal hydroxide loaded resin for ammonia removal from solutions containing high salinity by ligand exchange: Stability of metal ions during decomplexation of ammonia ligand

Abstract

Ligand exchange of ammonia with ammine-complexing transition metals loaded on the substrate has received more attention for removing ammonia from solutions containing high salinity. However, the stability between transition metal and substrate was destroyed by the desorbent in the process of the ligand exchanger recycling and ammonia ligand decomplexation, leading to metal elution and reducing the adsorption competency of the ligand exchanger. Herein, metal(ion)-loaded resins (Me(ion)-LR) were prepared and the stability of metal ions during the three-round ammonia adsorption–desorption process was studied. The results showed the ammonia adsorption capacity of Cu2+-D751, Cu2+/Ni2+-D751 and Cu2+/Zn2+-D751 resin were 5.39, 5.80 and 5.65 mg/g, respectively and the shedding percent of Cu2+ is lower than that of Ni2+ and Zn2+. Aimed for the high ammonia selectivity and low metal ion dissolution, metal(ion)-loaded resins were modified with NaOH to obtain metal(hydroxides)-loaded resins (Me(hydroxides)-LR). The stability of metal ions during the three-round ammonia adsorption–desorption process was also investigated. Meanwhile, the mechanism of the Me(hydroxides)-LR for ammonia removal was explored. The results suggested that the Cu(OH)x-D751, Cu(OH)x/Ni(OH)x-D751 and Cu(OH)x/Zn(OH)x-D751 resin have higher ammonia adsorption capacity and reached 5.79, 8.25 and 7.94 mg/g, respectively. The shedding percent of Cu2+ and Zn2+ decreased obviously. Experimental and characterization results show that the ammonia removal by Me(hydroxides)-LR was primarily due to coordination complexation and electrostatic interaction.