Study On Removal Of Cd²⁺ In Aqueous Solution On Zeolite 4A

Heavy metal pollution is widely known as one of the most serious problems on the environment and human. In the view of further implementation of global sustainable development strategy, treatments for heavy metals in wastewater are of great significance to the environment. Cadmium is a water migration element and it is as known one of the most poisonous heavy metal pollutants. The conventional methods for heavy metal removal from wastewater include co-precipitation of Hydroxides, ferrite technique, ion-exchange resins, membrane treatment and adsorption method. All the methods had its relative merits and sphere of application.Natural zeolite and zeolite 4A was analyzed as adsorbent to remove Cd2+from polluted water, and the effects of zeolite powder dosages, contact time, temperature and pH on the removal of Cd2+were investigated. The result showed that larger zeolite dosages, longer cintact time, higher pH can make better removal efficincy of Cd2+ by natural zeolite and zeolite 4A. the removal rate of Cd2+in aqueous solution was up to 99% after 30min at 40℃when a 100ml aqueous solution of Cd2+(100mg/L) was adsorbed by O.lg zeolite 4A and The sorbent exhibited good sorption potential for Cd2+with a peak value at pH 6.0-7.0.Adsorption mechanism of Cd2+on natural zeolite and zeolite 4A was discussed from the sorption thermodynamic and sorption kinetics. The sorption kinetics can be well described by the second-order kinetics, which can predict the effect of time on the adsorption. The sorption of natural zeolite and zeolite 4A followed the Langmuir sorption model better, the correlation coefficient was 0.9949 and 0.9918, respectively. The zeolite 4Ahad a 142.86mg·g-1 adsorption capacity for Cd2+ and the natural zeolite had a 17.6mg·g-1 adsorption capacity.Under the experimental condition, Pb2+ exhibited the highest effect on the sorption of Cd2+ on zeolites 4A and the decreasing order of the counter ion effect is Pb2+>Mg2+>Ca2+-Cu2+. When 0.5g·L-1 zeolite 4A was added, the removal rate of Cd2+ reached 99% at an initial Cd2+ concentration of 50mg·L-1 and competitive ions concentration of 10mg·L-1.When the zeolite 4A was regenerated by saturated NaCl solution, the removal efficiency of Cd2+had been decreased by 8.2% after recycling 5 times. However, the zeolite 4A had a 127.72mg·g-1 adsorption capacity for Cd2+...