Removal Performance For Cu(Ⅱ) With Dithiocarboxyl Corn Straw As Heavy Metal Adsorbent

This article discusses the use of modified corn straw as an adsorbent for the removal of copper ions from wastewater.Copper ion is often present in wastewater from industries,such as electrical,mechanical,and parts manufacturing.Various methods for treating wastewater containing copper include chemical precipitation,ion exchange,membrane separation,adsorption,and microbiological methods.Adsorption is particularly suitable for treating low-concentration copper wastewater,as it is cost-effective and does not cause secondary pollution.The researchers have found that corn straw,which is abundant in China,can be modified to improve its adsorption properties by introducing amino,carboxyl,and thiol groups.The study used a modified corn straw adsorbent,called dithiocarboxyl corn straw(DTCS),and tested its performance under different conditions,including reaction container,oscillation rate,adsorption temperature,initial pH,and copper concentration.The researchers also used Plackett-Burman and response surface methods to optimize the adsorption conditions and evaluate the effects of coexisting ions on the adsorption performance of DTCS.The study found that DTCS was effective in removing copper ions from wastewater,and the optimal adsorption conditions were identified.The researchers also found that the adsorption process of DTCS involved physical adsorption,chemical adsorption,and electrostatic interaction.Finally,the study examined the feasibility of reusing filter liquor generated in the preparation of DTCS.The main results are as follows:(1)The optimal adsorption conditions for Cu(II)by DTCS were obtained using a single-factor method.The reaction container was an iodine bottle,shaking speed was 200r/min,adsorption temperature was 30℃,adsorption time was 100 min,and the initial pH of the water sample was 6.Under these conditions,when 9 g/L of DTCS was added to a water sample with an initial Cu(II)concentration of 50 mg/L,the removal rate of Cu(II)by DTCS could reach 98.96%.(2)The adsorption process of DTCS on Cu(II)followed a pseudo-second-order kinetic model,and the adsorption behavior conformed to the Freundlich isotherm adsorption model.The thermodynamic parameters of adsorption,?~θand?~θ,were positive and negative,respectively,at various temperatures.Characterization analysis before and after adsorption of Cu(II)by DTCS was performed using Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),and energy-dispersive X-ray spectroscopy(EDS).The results indicated that physical adsorption,chemical adsorption,and electrostatic interaction coexisted during the process of DTCS adsorption of Cu(II).Physical adsorption may involve hydrogen bonding and van der Waals forces,while chemical adsorption involves disulfide carboxyl groups,mercaptans,hydroxyl groups,and so on.(3)Using Plackett-Burman experiments,it was found that the significant factors affecting DTCS adsorption of Cu(II)were adsorption temperature and the initial pH of the water sample when the DTCS dosage was 1 g/L,3 g/L,and 5 g/L.The central points of the significant factors at each dosage were obtained through the steepest ascent experiments and were found to be an adsorption temperature of 40℃and an initial pH of 5 for the water sample.(4)The optimal adsorption conditions for Cu(II)by DTCS were obtained using response surface methodology with a central composite design(CCD)experiment,which were as follows:the reaction container was an iodine bottle,the shaking speed was 200 r/min,the adsorption temperature was 50℃,the adsorption time was 120 min,and the initial pH of the water sample was 5.5.Under these conditions,when 1 g/L,3 g/L,and 5 g/L of DTCS were added to a water sample with an initial Cu(II)concentration of 50 mg/L.The corresponding removal rates of Cu(II)were 43.93%,74.22%,and 89.51%,respectively.The corresponding adsorption amounts were 21.96 mg/g,12.37 mg/g and 8.95 mg/g,respectively.(5)The influence of coexisting ions on the performance of DTCS adsorption for Cu(II)varied greatly,mainly inhibiting the adsorption performance of DTCS.Among them,the effect of inorganic ions was relatively small,while EDTA and sodium citrate in organic matter could greatly inhibit the adsorption performance for Cu(II)by DTCS.(6)The maximum removal rate of Cu(II)using the filtrate generated during DTCS preparation process could reach 97.03%for treating a water sample with an initial Cu(II)concentration of 25 mg/L and an initial pH of 3.Therefore,the filtrate could be used as a flocculant to remove Cu(II)from water.