Adsorption And Interaction Of Cu²⁺,pb²⁺,zn²⁺ On BS-12 Amphoteric Modified Bentonite

Amphoteric modified clay minerals as adsorbents which can simultaneously remove compound pollution of organic matters and heavy metals had received extensive attention and research.However these researches on heavy metals almost focused on the adsorption of single metal ion.The actual environmental pollution was usually not caused by single metal ion,but a composite pollution system formed by the simultaneous existence of multiple heavy metals,and there were interactions between the coexisting heavy metals.Therefore,it is of practical significance to study the adsorption and interactions of composite heavy metals on amphoteric modified clay minerals for the application of amphoteric modification on water heavy metals pollution remediation.In this paper,the bentonite was used as modified substrate,the dodecyl dimethyl betaine?BS-12?was used as amphoteric surfactant and the Cu²⁺,Pb²⁺and Zn²⁺were used as heavy metals pollutant.The adsrption characteristics of the three heavy metals in single and multi-heavy metals systems?Cu,Pb,Zn,Cu-Pb,Cu-Zn,Pb-Zn,Cu-Pb-Zn?on the unmodified and BS-12 modified bentonites were reasearched,and also studied the efffects of temperature,p H and ionic strength on the heavy matals adsorption.In order to provide theory and application basis for BS-12 amphoteric modified bentonite on multi-heavy metals pollution,the adsorption mechanism of Cu²⁺,Pb²⁺,Zn²⁺on unmodified and BS-12 modified bentonites were explored according to the FTIR analysis before and after heavy metals adsorption.The main conclusions of the paper were as follows:?1?In Cu,Pb and Zn single system,the adsrption capacities of the three heavy metals on CK?representing unmodified bentonite?,50BS-12,100BS-12,150BS-12?representing the modified bentonites that the amount of amphoteric surfactant were equivalent to the 50%,100%and 150%percents of bentonite's CEC,respectively?were in the order of Pb²⁺>Cu²⁺>Zn²⁺;The adsorption capacities of Cu²⁺,Pb²⁺and Zn²⁺on the four adsorbents all followed the sepuence of 150BS-12>100BS-12>50BS-12>CK.Therefore the 150BS-12represented the amphoteric modified bentonite with the best adsorption capacity to heavy metals.And among them,50BS-12 and 100BS-12 had more significant improvement on the adsorption capacity of Pb²⁺,and 150%BS-12 modification was more conducive to Cu²⁺adsorption;The increase of temperature was more conducive to the adsorption of Cu²⁺and Pb²⁺,but not to the adsorption of Zn²⁺.The increase of p H and the decrease of ionic strength were conducive to the adsorption of Cu²⁺,Pb²⁺and Zn²⁺.?2?In Cu-Pb,Cu-Zn,Pb-Zn binary and Cu-Pb-Zn ternary systems,the adsorption capacities and competition coefficients of three heavy metals on CK and 150BS-12?the amphoteric modified bentonite with the best adsorption capacity to three metals which was selected by single heavy metal system?presented the order of Pb²⁺>Cu²⁺,Cu²⁺>Zn²⁺,Pb²⁺>Zn²⁺and Pb²⁺>Cu²⁺>Zn²⁺,which were consistent with the results of single system;The adsorption capacities of Cu²⁺and Pb²⁺on 150BS-12 were still greater than CK,and the adsorption capacity of Zn²⁺on 150BS-12 was smaller than CK.However,the sum of the adsorption capacities of two or three metal ions in the binary or ternary system were still in the order of 150BS-12>CK,confirming that the modification of 150%BS-12 had improvement on heavy metals adsorption;The increase of temperature and p H were more favorable to the competitive adsorption of Cu²⁺,while the increase of ionic strength was more unfavorable to the competitive adsorption of Zn²⁺.?3?Competitive adsorption on the adsorption sites leaded to the interactions between metal ions.In Cu-Pb binary system,Cu²⁺and Pb²⁺had an antagonistic effect on each other's adsorption;In Cu-Zn and Pb-Zn systems,Cu²⁺and Pb²⁺had an antagonistic effect on the adsorption of Zn²⁺,while Zn²⁺had little effect on Cu²⁺and Pb²⁺and even showed a slight promotion effect;And in Cu-Pb-Zn ternary system,the three metal ions were mutually antagonistic.?4?The FTIR analysis of CK and 150BS-12 modified bentonite before and after adsorption of heavy metals showed that the hydroxyl group?-OH?group on bentonite and the hydroxyl group?-OH?,quaternary amino groupa?-NR₄?and carboxylate group?-COO^-?on BS-12 modified bentonite were the main chemisorption sites of metal ions.Among them,Pb²⁺had stronger binding ability with the-OH and-NR₄groups than Cu²⁺and Zn²⁺,while the-COO^-group was more inclined to combine with Cu²⁺;The chemical adsorption was dominant in the adsorption of Cu²⁺which had stronger binding ability with-COO^-of BS-12.The adsorption of Zn²⁺was dominated by electrostatic attraction and ion exchange,but its binding ability with the two adsorption sites were weaker than Cu²⁺and Pb²⁺.While Pb²⁺had stronger binding ability with the four adsorption sites of electrostatic attraction,ion exchange,the-OH groups of bentonite and the-NR₄group of BS-12.