Study On The Removal Efficiency And Mechanism Of Cu From Industrial Wastewater By The Similar To Schwertmannite

With the development of society,the demand of metal smelting and electroplating industry is increasing,resulting in the increase of copper content in wastewater.Cu²⁺has high solubility and toxicity,and is easy to have organic matter in the soil,endangering human health and ecological environments.At present,the main method of processing Cu²⁺in industrial wastewater has an adsorption method,ion exchange method,and chemical precipitation method.Among them,schwertmannite is one of the common adsorbents.Schwertmannite is derived from acidic mine wastewater,which belongs to secondary hydroxy sulfate minerals,but needs to regulate the p H of the wastewater and take 24 h pre-chemical synthesis.There is a problem with long processing cycle,and the adsorption effect is poor.To this end,this study is proposed to embed CaCl₂ and Na₂SiO₃ during the FeSO₄·7H₂O and H₂O₂synthesis of the schwertmannite,generate a kind of mineral removal Cu²⁺,thereby shortening the treatment cycle,and increasing the processing level.The research content and results are as follows:1.Study on the influencing factors of treating copper in industrial wastewater with the similar to schwertmannite.FeSO₄·7H₂O,H₂O₂,CaCl₂ and Na₂SiO₃ were added into 400 mL of 150 mg/L copper containing simulated wastewater.Under the conditions of 20℃,650 r/min,0.50mmol/L complexing agent and 1.50 mmol/L coexisting ions,the magnetic stirring test was ccarried out for 10 min.The effects of initial p H,temperature,initial copper content,complexing agent concentration and coexisting ion concentration on copper removal of similar to schwertmannite were investigated.The results are as follows:L₁₆（4⁴）orthogonal test was carried out with the type of reactants as the factor and total content of reactants（concentration of reactants）as level.The optimal reactant component concentration ration was obtained as follows:0.5 g/L FeSO₄·7H₂O,1.01mL/L H₂O₂,0.58 g/L CaCl₂ and 3.25 g/L Na₂SiO₃.At this time,the removal rate of copper was 86.68%,and the copper content was 19.89 mg/L.When the initial p H increases from 2.0 to 5.0,the copper content decreases from64.77 mg/L to 19.50 mg/L,and the removal rate of copper increases by 30.18%.The increase of initial p H can effectively improve the removal level of copper.When the temperature increases from 20℃to 40℃,the copper content decreases from 22.70 mg/L to 17.90 mg/L,and the removal rate of copper increases by 3.71%.The effect of temperature rising on copper removal is weak.When the initial copper content increases from 50mg/L to 300mg/L,the copper content increases from 17.74 mg/L to 31.27 mg/L,and the copper removal rate decreases by 9.40%.The increase of initial copper content will inhibit the removal of copper.When the concentration of complexing agent increased from 0.7 mmol/L to 1.5mmol/L,the copper content increased from 38.83mg/L to 79.82 mg/L,and the removal rate of copper decreased by 27.51%.The increase of complexing agent concentration would significantly reduce the removal level of copper.When the concentration of coexisting ions increases from 5 mmol/L to 45 mmol/L,the copper content increases from 28.36 mg/L to 33.09 mg/L,and the removal rate of copper decreases by 3.15%.The increase in the concentration of coexisting ions will inhibit the removal of copper.2.Study on the removal efficiency of copper from industrial wastewater by the similar to schwertmannite.（1）The treatment effect of copper in industrial wastewater by similar to schwertmannite.According to test 1,the best test conditions were p H 5.0,40℃,50 mg/L copper,0.50 mmol/L complexing agent,1.50 mmol/L coexistence ion.Under these conditions,0.5 g/L FeSO₄·7H₂O,1.01 mL/L H₂O₂,0.58 g/L CaCl₂ and 3.25 g/LNa₂SiO₃ were added to 400 mL copper containing simulated wastewater with a concentration of 50mg/L to similar to schwertmannite,and the magnetic stirring test was carried out for 10min at a rotating speed of 650 r/min.The residual copper content was 1.97mg/L,and the removal rate was 96.27%.Under the same wastewater conditions,the actual wastewater with copper content of 74.98mg/L was treated with similar to schwertmannite,and the residual copper content was 1.67mg/L,and the removal rate was 97.99%.The dissolution rate of copper is 1.98%in 0～1 d after the treatment of simulated wastewater by similar to schwertmannite,and remain unchanged in the next 19 d.After the actual wastewater was treated by similar to schwertmannite,the dissolution rate of copper in 0～1 d was 0.29%,and there was no change in 19 d after that,which indicated that the removal of copper from industrial wastewater by similar to schwertmannite had a good stability.（2）The treatment effect of copper in industrial wastewater by schwertmannite.The schwertmannite was prepared by adding 22.24 g/LFeSO₄·7H₂O and 12.00mL/LH₂O₂ for 24 h.Under the same conditions,5.45 g/L of schwertmannite was added to the copper containing simulated wastewater,and the 3 h magnetic stirring test was carried out at a rotating speed of 650r/min.The residual copper content in the wastewater was 44.37 mg/L,and the removal rate was 11.26%.Under the same conditions,the actual copper containing wastewater with a concentration of 74.98 mg/L was treated,and the residual copper content was 71.25 mg/L,and the removal rate was4.97%.Compared with similar to schwertmannite,they were reduced by 85.01%and93.02%.The dissolution rate of copper is 21.04%in 0～1 d after treatment of simulated wastewater by schwertmannite,and remain unchanged in 19 d.After the actual wastewater was treated with schwertmannite,the copper dissolution rate was 16.62%in 0～1 d,and there was almost no change in the next 19 d.The dissolution rate of copper increased by 19.06%and 16.33%,respectively,compared with that of similar to schwertmannite,indicating that the copper removal efficiency and stability of similar to schwertmannite are significantly better than that of schwertmannite.3.Study on the mechanism of removing copper from industrial wastewater by similar to schwertmannite.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）and Fourier transform infrared spectroscopy（FTIR）were used to explore the mechanism of removing copper from industrial wastewater by similar to schwertmannite.The results are as follows:Compared with schwertmannite,the similar to schwertmannite provide more adsorption sites to adsorb Cu²⁺,and Cu²⁺is adsorbed on the minerals through coprecipitation.At the same time,it can be fixed on the mineral surface by isomorphism substitution and can coordinate with the rich functional groups of minerals to achieve the purpose of removal.The SEM results show that the mineral phase gradually tends to be stable after 1min of copper treatment,indicating that Cu²⁺is removed by similar to schwertmannite within 1min,which is much shorter than the treatment time of schwertmannite.The results show that the main mechanism of copper removal is coprecipitation,and the initial p H has the most significant effect on the removal of copper.Under the best experimental conditions,the residual copper content（1.97 mg/l,1.67 mg/l）of simulated and actual wastewater treated by similar to schwertmannite can meet the 2mg/L requirement of"Water Quality Standard for Sewage Discharge into Urban Sewers"（GB/T 31962-2015）.The results of actual wastewater and simulated wastewater are close to each other,which indicates that similar to schwertmannite and the model of treating simulated wastewater containing copper can be replicated for practical engineering application.