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ADSORPTION OF CADMIUM FROM AQUEOUS SOLUTIONS ON ACTIVATED CARBON PREPARED FROM S.ALTERNIFLORA

Activated carbons were prepared from S.alterniflora by phosphoric acid activation using various acid/precursor impregnation ratios(0.5—3.0) and different activation temperatures(400 ℃—700 ℃),and were used for the adsorption of cadmium ions from aqueous solution.Adsorption isotherms were determined from solutions with different initial concentrations.The adsorption mechanism,influence factors,favorable activation conditions,etc,were investigated.This study confirmed that the impregnation ratio between H3PO4 and precursor,and activation temperature are important factors affecting the adsorption capacity of the activated carbons.An impregnation ratio and an activation temperature around 1 g H3PO4/g S.alterniflora and 700 ℃,respectively,are recommended as the best combination of operating conditions to prepare activated carbons for cadmium adsorption.In addition,the adsorption capacity calculated from the Langmuir isotherm was 47.85 mg·g-1.The results showed that adsorption of cadmium depends on the chemistry of the surface of activated carbon rather than on its surface area or pore structure.It was found that the ion exchange mechanism was involved and played an important role in the adsorption.The removal rate increased with pH from 2 to 4 and remained constant up to pH 4.