Competitive Adsorption Between K⁺,Na⁺,Ca²⁺and Cr⁶⁺ On Activated Carbon And Its Application

Among the methods to dispose of waste water containing chromium,the adsorption method receives much concern due to the advantages of a wider range of adsorbent selectivity,small secondary pollution and good treatment effect.The activated carbon as a kind of environmentally friendly adsorbent,because of its wide sources,high security,stronger adsorption to the heavy metal ions,become a research focus.The researchers focus on activated carbon adsorption of heavy metal ions.However,actual waste water composition is very complicated,which contains many other coexisting light metal ions in addition to heavy metal ions.Based on those,this paper takes simulated waste water containing heavy metal Cr⁶⁺ion and coexisting light metal ions K⁺、Na⁺、Ca²⁺for research object.Effect on active carbon adsorption Cr⁶⁺processing in three coexisting ions was studied.Competitive adsorption behavior of K⁺、Na⁺、Ca²⁺and Cr⁶⁺on activated carbon and thermodynamics and kinetics of activated carbon adsorption of Cr⁶⁺in the coexistence system was analyzed;Finally,treatment technology of galvanized sheet waste water which came from factory were studied.The main results are as follows:（1）K⁺,Na⁺,Ca²⁺ions joining respectively make percentage of Cr⁶⁺removal by activated carbon adsorption fell by 9.68%,10.61%,44.16%,the influence order is about Ca²⁺>Na⁺>K⁺.Falling of percentage of Cr⁶⁺removal in three ions and double ions system was greater than single ion system,there were effect coupling enhancement of percentage of Cr⁶⁺removal by activated carbon in coexisting three ions and double ions.There is no competition adsorption between K⁺、Na⁺and Cr⁶⁺,the reason why percentage of Cr⁶⁺removal reduced by activated carbon adsorption in K⁺、Na⁺system is that Near the active site of K⁺,Na⁺and Cr⁶⁺caused by electrostatic repulsion.There is competition adsorption between Ca²⁺and Cr⁶⁺,because it has active site adsorbing Ca²⁺on the surface of activated carbon,hydration radius of Ca²⁺is the smallest among K⁺,Na⁺,charge is the most,effect on electrostatic repulsion of Cr⁶⁺and electrostatic force of active site is the strongest,therefore percentage of Cr⁶⁺removal is the lowest.Process adsorbing Cr⁶⁺between active site on the surface of activated carbon is chemical adsorption,however,Process adsorbing Ca²⁺between active site on the surface of activated carbon is physical adsorption.（2）Adsorption Cr⁶⁺process by activated carbon in K⁺,Na⁺,Ca²⁺coexistence system was fitted by Langmuir,Freundlich and Temkin model,fitting correlation coefficient is 0.997,0.994,0.799,respectively.Correlation coefficient of Langmuir is greater than Freundlich and Temkin model,it showed that Langmuir model more accord with adsorption process of Cr⁶⁺by activated carbon.AdsorptionCr⁶⁺by activated carbon mainly occurred in the surface of activated carbon,it belongs to monolayer chemical adsorption.（35）G<0 of adsorption process of Cr⁶⁺by activated carbon,it showed that adsorption process is spontaneously.AdsorptionCr⁶⁺process by activated carbon was fitted by pseudo first-order,pseudo secondary and internal diffusion dynamics model,fitting correlation coefficient is0.999,0.978,0.91,respectively.,it showed that pseudo secondary model more accord with adsorption process of Cr⁶⁺by activated carbon,it controlled by the chemical mechanism,belongs to the chemical adsorption monolayer.（3）For galvanized sheet waste water,which came from factory,was absorbed by activated carbon was modified by Using ethanol and acetic acid,The process for modification optimal temperature is 50℃,time is 40 minutes.Modified activated carbon has new vibration peak at 874 cm^-1,it showed that new functional groups were introduced by modification.Unprocessed waste water was adsorbed by activated carbon,percentage of Cr⁶⁺removal is 9.05%before disposal waste water,however,it is25.5%after disposal waste water.Remove silicon and calcium from galvanized sheet waste water was by addition sulfuric acid,the waste liquid with sulfuric acid ratio is100:0.4.Waste water treated was adsorbing by modified activated carbon,Optimal dosing quantity of active carbon is 0.4g,optimal solution pH is3,optimal temperature is 30℃,maximum percentage of Cr⁶⁺removal is up to 98%.Optimal desorption time of activated carbon containing Cr⁶⁺is 60 min in the ultrasonic cleaner can by using barium chloride solution.percentage of Cr⁶⁺removal is up to 50%by desorbed activated carbon.