Zhigang Dan

Evaluation of polyacrylic anion exchange resins on the removal of Cr(VI) from aqueous solutions

This study evaluated the multi-cycle Cr(VI) removal performance of four polyacrylic anion exchange resins (D730, D314, 312 and 213) with different functional groups and porosities based on a fixed-bed column operation. Particular emphasis was given to the effect of oxidation fouling on the ion exchange properties and performance of polyacrylic resins. The functional groups had significant effects on the exchange capacity, adsorption rate, regeneration efficiency, and oxidative stability for Cr(VI) removal. Oxidation fouling on the polyacrylic resins had a significant influence on the removal of Cr(VI). After a 10-cycle operation, due to the oxidation of resins, the adsorption capacities of D730, 213, D314 and 312 resins decreased by 19.8, 21.7, 13.4 and 15.3%, respectively. The results of the Fourier transform infrared rays (FT-IR) analyses showed that the cleavage of C–N and C–C bonds occurred on the polyacrylic resins during the Cr(VI) removal process, indicating the degradation of the resin functional group and matrix. This work provided an understanding of exchange behavior and oxidation fouling of Cr(VI) on different polyacrylic resins, and should result in more effective applications of ion exchange for Cr(VI) removal from solutions.

The oxidative degradation of polystyrene resins on the removal of Cr(VI) from wastewater by anion exchange

Cr(VI) is a powerful oxidant and is capable of oxidizing most of the organic materials. Therefore, it is possible for Cr(VI) to oxidize the polymeric resins and change the sorption properties of the resins on the removal of Cr(VI) from wastewater by anion exchange. In this study, three polystyrene resins (D201, D202, and D301) with different functional groups (-N(+)(CH3)3, -N(+)(CH3)2(C2H4OH), and N(CH3)2) were assessed on oxidation stability for Cr(VI) removal from wastewater in fixed-bed column experiments. After a 10-cycle operation, due to the oxidation of the resin, the sorption capacity of D201, D202, and D301 resins decreased by 23.5, 29.3, and 17.3%, when approximately 20-34%, 31-50%, and 18-30% of Cr(VI) was reduced to Cr(III) during each cycle respectively. The results of the Fourier transform infrared spectroscopy (FT-IR) showed that both the cleavage of CN and the formation of CO bonds occurred on the polystyrene resins during the Cr(VI) removal process. The resin simulation experiments further validated the oxidation of CC and CN bonds connected with phenethyl groups. Based upon the results from column operations and the resin simulated experiments, the oxidation mechanism of the polystyrene resin was proposed.

Reductive recovery of manganese from low-grade manganese dioxide ore using toxic nitrocellulose acid wastewater as reductant

The hydrometallurgical strategy of extracting Mn from low-grade Mn ores has attracted attention for the production of electrolytic manganese metal (EMM). In this work, the reductive dissolution of low-grade MnO2 ores using toxic nitrocellulose acidic wastewater (NAW) as a reductant was investigated for the first time. Under the optimized conditions of an MnO2 ore dosage of 100 g·L−1, an ore particle size of −200 mesh, concentrated H2SO4-to-NAW volume ratio of 0.12, reaction temperature of 90°C, stirring speed at 160 r·min−1, and a contact time of 120 min, the reductive leaching efficiency of Mn and the total organic carbon (TOC) removal efficiency of NAW reached 97.4% and 98.5%, respectively. The residual TOC of 31.6 mg·L−1 did not adversely affect the preparation of EMM. The current process offers a feasible route for the concurrent realization of the reductive leaching of Mn and the treatment of toxic wastewater via a simple one-step process.