Highly cost-efficient sorption and desorption of mercury ions onto regenerable poly(m-phenylenediamine) microspheres with many active groups

Abstract

Abstract Poly(m-phenylenediamine) (PmPD) microspheres were productively and sustainably synthesized by a facile one-step chemical oxidative polymerization of m-phenylenediamine with ammonium persulfate in pure water without any acid or alkali. A comprehensive characterization of the structures, morphology, and nature of PmPD microspheres suggested that they exhibited highly chemical/thermal resistance and strong Hg(II) adsorbability. The batch static sorption/desorption of mercury ions were systematically optimized by adjusting the sorption/desorption time and temperature, mercury-ion concentration, sorbent dosage, and the species, concentration and dose of desorbents. The microparticles exhibit high Hg(II) sorption capacity up to 1499.2 mg/g at an initial Hg(II) concentration of 1986 mg/L, high Hg(II) partition coefficient up to 5040 mg/(g.μM) at an initial Hg(II) concentration of 20 mg/L, and high initial sorption rate up to 763.3 mg/(g.min). The dynamic sorption results suggest that the breakthrough and saturation times of the column loaded with the microparticles toward 1.99 mM Hg(II) solution at the flow rate of 1 mL/min are 19.8 h and 58.0 h, respectively. After 5 dynamic sorption-desorption cycles, the column efficiency is still high, indicating good reusability. A sorption mechanism including the first reduction from mercury-ion to mercurous-ion by amino and imino groups, and the second complexation and ion exchange of mercurous-ions is proposed. Without the pollution caused by the preparation or part solubility of sorbents themselves, the PmPD microspheres are cost-effectively and eco-benignly applicable to elimination and recovery of mercury ions in wastewater. This generates a unique solution to sustainable problems of sorbents themselves.