Method And Mechanism Of New Iron-containing Composite Materials For The Treatment Of Cr(Ⅵ)-containing Wastewater

With the development of society,the harmful effects of Cr（Ⅵ）in water bodies on the environment and humans have become more and more serious.Therefore,in this paper,based on iron,a variety of new iron-containing composite materials have been prepared to make it more efficient to remove Cr（Ⅵ）in water.The specific research is as follows:（1）Starch coated nanoscale zerovalent iron（S-nZⅥ）was immobilized in activated carbon（AC）and its Cr（Ⅵ）removal characteristics were studied.Macroscopic evidence and mechanism analysis proved that S-nZⅥ and AC were closely linked and mutual complementary,which raised Cr（Ⅵ）removal from water by 18.39%due to the synergistic effect.The stable Cr（Ⅵ）scavenging for S-nZⅥ-AC increased with reaction time and reached the maximum capacity of 72.542 mg/g in 390 min.The removal of Cr（Ⅵ）by S-nZⅥ-AC followed pseudo-second-order kinetics.S-nZⅥ-AC might be a potential composite material for of in Cr（Ⅵ）purification and detoxification from water for its efficiency and stability.（2）Nano-zero-valent iron biochar（nZⅥ-ASBC）derived from almond shell was used for hexavalent chromium（Cr）removal.Experiments showed that pH was the main factor（P<0.01）that affected the experimental results.At a dosage of 10 mg·L^-1 and pH of 2–6in the first 60 min,nZⅥ-ASBC exhibited a removal efficiency of 99.8%,which was approximately 20%higher than the removal yield at pH 7–11.Fourier transform infrared spectroscopy results indicated N-H was the main functional group that influenced the chemisorption process.Thermodynamic studies showed that the reaction was exothermic and spontaneous at low temperatures（T<317 K）.Various interaction mechanisms,including adsorption and reduction,were adopted for the removal of Cr（Ⅵ）using the nZⅥ-ASBC composite.（3）This study explored a green method for aqueous hexavalent chromium（Cr（Ⅵ））reclamation by waste steel slag enhanced by natural pyrite（NP-SS）.Compared with the sole natural pyrite,more efficiently Cr（Ⅵ）is removed by NP-SS at initial pH value ranging from 1 to 8,while the final pH value was around 7.5.Results indicated that Cr（Ⅵ）in the solution was reduced to Cr（Ⅲ）by Fe²⁺on the surface of pyrite,which could be further bound with the supersaturated calcium silicate hydrate on the surface of steel slag.In addition,the stearic acid anions existing on the surface of steel slag could promote the adsorption of Cr（Ⅲ）thus forming chromium stearate.This study provides three new methods for the removal of chromium,and all of them show good removal ability for the removal of Cr（Ⅵ）.The removal of Cr（Ⅵ）by modified nano-zero-valent iron depends on oxidation-reduction and adsorption,while the removal process of Cr（Ⅵ）by NP-SS involves flocculation in addition to the mechanism of oxidation-reduction and adsorption.The reduced Cr（Ⅲ）can also be well fixed on the surface of NP-SS,effectively preventing the secondary pollution of Cr（Ⅲ）caused by air oxidation.This provides a new method for the removal of heavy metal chromium,and also provides theoretical support for practical applications.