Entrapment Of Nanoscale Zero-valent Iron In Carboxymethyl Chitosan Beads For Hexavalent Chromium Removal From Wastewater

In the modern manufacturing industry,Hexavalent chromium which was widely used in Leather industry, Textile industry, Dyeing industry and Auto industry et al, And it played an important role to the social and economic development. However, some factories discharged wastewater containing chromium which unreasonable caused serious environmental pollution. Hexavalent chromium which raised the rate of oncogenic mutation seriously harmed to human health and animal and plant, Hence Environmentalists focused on how to solve the problem of hexavalent chromium pollution effectively. In recent years, Environmental nanomaterials was developing rapidly, Especially nano zero-valent iron(n ZVI). it was easy to prepare n ZVI which had high reactivity, therefore n ZVI became one of the hottest environmental remediation technology. In the fact, n ZVI faced severe challenges because of easy reunion and poor stability.To solve above problems, in this paper we used carboxymethyl chitosan as coating agent, and prepared entrapment of nanoscale zero-valent iron in carboxymethyl chitosan beads(CMCS-Fe0) which removed hexavalent chromium of liquid. This paper discussed preparation conditions of CMCS-Fe0, and Investigated its removal ability of hexavalent chromium in the batch experiments, Further researched the kinetics and mechanism about removal hexavalent chromium by CMCS-Fe0. The main research content was as follows:This work aimed to study some factors about carboxymethyl chitosan concentration, the dosages of n ZVI, cross-linking agent(calcium chloride) concentration, cross-linking time to investigate the optimized preparation conditions of CMCS-Fe0 for hexavalent chromium removal, and it was the better preparation parameters that were 5 wt% of carboxymethyl chitosan concentration, 1.0g n ZVI, 9wt% cross-linking agent(calcium chloride) concentration and 1h cross-linking time. in this artcle, we analyzed CMCS-Fe0 by TEM( transmission electron microscopy), and the results showed that n ZVI size distribution range was 7 ~ 58 nm, and the average particle size was 25.35±7.11 nm. In the same way, we analyzed CMCS-Fe0 by VSM(vibrating sample magnetometer) to learn that the saturation magnetization of CMCS-Fe0 which was far less than 67.8emu/g of n ZVI was 23.5emu/g, But fortunately, the CMCS-Fe0 can still be adsorped by the magnet.The article investigated the dosages of CMCS-Fe0, initial hexavalent chromium concentration, p H and temperature on the Influence of removal of hexavalent chromium efficiency. On the one hand, the study found that improvement of the dosages of CMCS-Fe0 and the rise of temperature all can improve the removal efficiency of hexavalent chromium. Increasing from 0.04 g/L to 0.28g/L, The corresponding removal rate of hexavalent chromium respectively was 86.32%, 95.89%, 100%, 100%, 100%. At 25, 40, 50℃, removal rate was 92.10%, 97.05%, 98.80% after 2h. On the other hand, Initial hexavalent chromium concentration and p H had inhibitory effect on removal of hexavalent chromium. When initial concentration increased from 5mg/L to 50mg/L, the removal rate reduced from 100%to 65.46%. similarly, When the initial solution p H increased from 3 to 11, Removal rate of hexavalent chromium was reduced from 100% to 91.33%.This paper examined the dynamics of removal of hexavalent chromium, and dicussed the dosages of CMCS-Fe0、initial hexavalent chromium concentration、p H and temperature about the relationship of the Kobs. The results clearly showed that the dosages of CMCS-Fe0 and reaction temperature was positively related to the Kobs. When the quantity of n ZVI increased from 0.04 g/L to 0.28g/L, the Kobs increased about eight times. in the same way, When the reaction temperature increased from 25 ℃to 50 ℃, the Kobs increased 1.73 times, and the half-life reduced from 0.65 h to 0.37 h. However, initial hexavalent chromium concentration and p H was negatively related to Kobs. When initial concentration was 15, 25, 50mg/L respectively, relevant Kobs was 0.58639 h-1, 0.3276 h-1, 0.08479 h-1. When p H boosted from 3℃ to 11 ℃, the Kobs reduced from 3.50789 h-1 to 0.3566 h-1, the half-life improved from 0.2 h to 1.94 h. the results indicated that the removal of hexavalent chromium by CMCS-Fe0 was in conformity with the first order reaction kinetics model.The results showed that adsorption, reduction, chelating the result of joint action about the removal of hexavalent chromium by CMCS-Fe0. In the process, a small amount of hexavalent chromium by adsorption on surface of CMCS-Fe0. XPS showed that more the ferric iron ions existed after the reaction than before, and XPS detected the presence of Cr2 p at the end of the reaction, which proved the hexavalent chromium was reduction by n ZVI. And XRD made clear that characteristic peak of n ZVI disappeared and characteristic peak of Fe-Cr Ox increased after the reaction which also implied existence of redox. FT-IR manifested carboxyl, amino and hydroxyl groups of CMCS had a chelation reaction with iron ion and chromium ion, and it showed that amino of CMCS-Fe0 also could chelate for molysite or chromic salt by XPS analysis.