Studies On The Adsorption Kinetics Of Phenol And Cd²⁺ In Amphiprotic Modified Bentonites

In the present study, the sorption kinetics characteristics and equilibrated adsorptioncapacity of phenol and Cadmiumionl on Dodecane-Betaine（BS-12） and Octadecane-Betaine（BS-18） modified bentonite along with the sorption mechanism were investigated at differentmodification ratio, temperature, ionic strength and pH.The conclusions were showed as follows:1. The adsorption equilibrium times of modified bentonite（BS-Bt） to phenol was120min.The experiment data fitted well with the results of pseudo-second-order kinetics, the fittedequilibrium adsorption obtained was close to experimental results. The adsorption capacityand velocity of phenol on modified bentonite was bigger than that of unmodified bentonite,and it increased with modification ratio increasing. The BS-Bt adsorption to phenol reachedthe balanced time in a short time; the phenol adsorption was bigger at high ionic strength; andhad obvious facilitation at the pH4-8, while when pH was bigger than8, the amount ofadsorption declined rapidly. The adsorption capacity of phenol on BS12-Bt was greater thanBS-Bt at same modified proportion.2.The adsorption velocity of unmodified and modified bentonite to Cd²⁺was fast and thetransition time of fast-low reaction time was within20min. The adsorption kinetics curvesbasically fitted with the pseudo-second-order kinetics. The adsorption velocity of modifiedbentonite for Cd²⁺increased with increasing modification ratio; the order of the Cd²⁺adsorption was40℃<30℃<20℃at temperature; the Cd²⁺adsorption was slower at high ionicstrength; The increase of pH was in favorable for increasing the Cd²⁺adsorption in pH4⁸.3. Pseudo-second-order kinetic model was the better adsorption model to describe theeffect of the composite solution, phenol and Cd²⁺exist at the same time, on modifiedbentonite.The adsorption velocity of BS12-Bt for phenol increased with increasingmodification ratio, and changed greate compared with the single solution in different ionicstrength. The adsorption velocity of BS12-Bt for phenol in composite solution was greaterthan that of in single solution.The adsorption velocity of BS12-Bt for phenol was bigger at high temperature; The effect of ionic strength was not big. In composite solution, theadsorption of phenol showed certain stimulative effect.4.In composite solution，the adsorption velocity of BS12-Bt and BS18-Bt to Cd²⁺increased with the modified proportion increasing. The adsorption velocity of BS12-Bt andBS18-Bt was in accordance with the change of ionic strength at the20℃, which was0.5mol·L-1<0.1mol·L-1<0.01mol·L-1. The phenol had certain impeding effect on the adsorptionof Cd²⁺.Under the different conditions, the trend of adsorption capacity and velocity for phenoland Cd²⁺was obtained, the results showed that the adsorption bentonite to phenol mainlyformed hydrogen bonding with oxhydryl in phenol and oxygroup in bentonite, this processwas a chemical action with high energy and low reaction-speed; the adsorption capacity andvelocity of Cd²⁺on bentonite was greater because ion exchange adsorption. The adsorption ofphenol on modified bentonite was the process of forming organic phase, that was the carbonchain formed on bentonite surface, amphotetic modification result in a portion of positivecharge adsorption site occupied, and which formed scanty water phase made adverse impactto the adsorption of Cd²⁺, while the complexation key combined hydroxy and amidogen onmodifier with Cd²⁺conductive to the adsorption.