| Ion-exchange technology was used to purify the industrial waste water containing heavy metal, which attained to the resource recycling of heavy metal. However the treatment of chromium-containing waste water by ion exchange technology still had the following deficiencies in actual application:(1) weak alkaline exchanger should be converted to Cl- form, leading to the increasing in the concentration of chlorine ion of recovery solution, and it had a great influence on the electroplated coating quality when returned to the electroplating factory.(2) weak alkaline exchanger could absorb a certain amount of cations(adsorption capacity was 1.5mmol/g), such as Cr3+ and Fe3+, which was easy to form insolubles or chelate with anion adsorption material when regenerated, causing the decrease of exchange capacity. The concentration of Cl- in chromate recovery solution were increasing(CCl- ≥ 2 g/L) when polyacrylonitrile(PAN) based polyamine fibers were converted to Cl- form; and the treated effluent were weak acidic(p H≈3) which couldn’t be discharged directly. Based on above reasons, the multi-column process was optimized to treat the industrial wastewater containing chromium using PAN based polyamine fibers. The experiment was designed to enhance the purity and concentration of chromate eluent, and primarily discussed the "pollution" mechanism for fibers, which would provide a novel recycling method for Cr(VI). The the main research content were as follows:(1) The goal of enrichment for Cr(VI) in recovery solution and selective filtering for SO42- and Cl- would be achieved, taking advantage of the selective adsorption between SO42- and Cl-, as well as the optimization of multi-column process through turning part of the PAN based polyamine fibers into Cl- form. The results showed that the process could significantly reduce the amount of hydrochloric acid(for 1/9) and the concentration of Cl- in the recovery solution(about 0.04 g/L), also the p H of effluent were close to neutral before breakthrough(CCr(VI)≦ 0.1 mg/L), which could be used directly as plating water.(2) The PAN based polyamine fibers were regenerated repeatly by Na OH solution with high concentration, which would enhance the utilization ratio of Na OH(savings of 52%) and the concentration of hexavalent chromium in recovery solution(about 48g/L), providing the conditions for the recycling of electroplating process.(3) The flow rate on the adsorption and regeneration showed a great impact on the present experimental conditions. The saturated adsorption capacity of fiber was larger when the adsorption flow rate was at 2m L/(g·min); the fibers were regenerated completely when the regeneration rate was between 0.5m L/(g·min) ~2m L/(g·min).(4) The stability of optimizing multi-column process was good. After several cycles of adsorption and regeneration, the PAN based polyamine fiber still kept excellent adsorption performance, which proved that the recovery technology of hexavalent chromium had good prospects for industrial applications.(5) The dosage and the concentration of the HCl solution, as well as the recovery temperature, time and flow rate, had been investigated in the recovery experiment, using the hydrochloric acid solution as fiber recovery agents. Results showed that the recovery was the best(recovery rate was more than 95%), when the concentration of the HCl solution was 3mol/L. |
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