Study On Desorption And Regeneration Of Granular Bentonite Compound Adsorbent By Reagents

Adsorption is one of the important methods of wastewater treatment, and the key of its successful application is the selection of appropriate adsorbent. Generally, the adsorbent will reach saturation state after a period of adsorption and so lose ability to remove pollutants. Therefore, it is necessary to regenerate adsorbent in order to restore its adsorption ability for re-use, so reducing wastewater treatment costs and enhancing the adsorbent utilization efficiency. This article investigated desorption and regeneration by reagents of granular bentonite compound adsorbent, which was a novel product invented by author's supervisor and his group. The compound adsorbent was first loaded by copper ion, then the effects on desorption and regeneration of reagent types, reagent concentration, desorption time, dosage of adsorbent, adsorbed copper ion amount, temperature, and pH were examined, and finally the mechanism of desorption of copper from bentonite compound adsorbent was studied. The conclusions could be obtained as follows:(1) Sulphuric acid, nitric acid, hydrochloric acid, sodium chloride, sodium hydroxide, sodium citrate and EDTA had a certain degree of desorption and regeneration ability to the bentonite compound adsorbent loaded with copper ion. Desorption ratio of copper was enhanced along with the increase of reagent concentration, but the changes was not apparent. Changes of regeneration ratio of bentonite compound adsorbent was consistent with the desorption ratio.(2) Reagent concentration, desorption time, dosage of adsorbent, adsorbed copper ion amount, desorption temperature and pH influenced desorption and regeneration of bentonite compound adsorbent with copper loading in some extent. Desorption time and pH had a relatively large effect on desorption and regeneration, while desorption temperature affected slightly.(3) Among all of the reagents, EDTA was the best eluent, nitric acid followed, and sodium chloride was the worst. The sequence of regenerating bentonite compound adsorbent loaded with copper was that EDTA> sodium chloride> nitrate.(4) It was found that Cu²⁺ desorption by nitric acid, sodium chloride and EDTA respectively could be described by pseudo-first-order kinetic, pseudo-second-order kinetic, Elovich equation and two-constant equation among which pseudo-first-order kinetic and pseudo-second-order kinetic were the best.(5) Cu-desorption by nitrate acid or EDTA was agreed with the Langmuir isotherm, and Cu-desorption by sodium chloride was agreed with Langmuir, Freundlich or Temkin isotherm. Cu-desorption by EDTA or nitrate acid was a spontaneous process, but it was not by sodium chloride.(6) XRD analysises showed that crystal-interlamination adsorption may be existed in the adsorption of Cu²⁺ by bentonite compound adsorbent and Cu²⁺ could be desorbed by nitric acid, sodium chloride or EDTA.