Studies On Copper Adsorption By Calcium Alginate From Sludge

The biosorption characteristics of copper onto dried Ca-alginates, which were extracted from four kinds of sludge, were investigated in batch system respectively. This paper focused on the influences of contact time, adsorbent state, solution initial pH, Cu²⁺ initial concentration and adsorbent concentration on copper sorption by four kinds of dried Ca-alginate. Sorption isotherms, sorption kinetics and Cu²⁺ desorptions were also investigate respectively. Sorption mechanism was inferred.Calcium alginate could be successfully made from aerobic granules, activate sludge, anaerobic granules and biofilm matrix with the yield of (395±13) mg/g, (198±12) mg/g, (243±12) mg/g and (208±17) mg/g, respectively.Sorption capacity of dried Ca-alginate ( dried at 60℃) , extracted from aerobic granules was evaluated higher than gel Ca-alginate and the dried Ca-alginate was studied further. The Cu²⁺ sorption process of four kinds of Ca-alginates all included a rapid stage and a slow stage, and reached equilibriums at 60min, 90min, 240min and 180min respectively. Cu²⁺ initial concentration, Solution initial pH and biomass concentration were critical for Cu²⁺ biosorption. The Cu²⁺ uptakes were 67.67 mg/g, 41.97 mg/g, 84.61 mg/g and 56.15 mg/g respectively, at pH 4, initial Cu²⁺ concentration of 100mg/L and Ca-sludge alginate dosage 0.7g/L.Accumulation of Cu²⁺ by four kinds of Ca-alginates all followed Langmuir adsorption isotherm better than Freundlich adsorption isotherm.The sorption kinetics'studies of Cu²⁺ showed that the pseudo-second-order model was more suitable to describe the sorption process than the pseudo-first-order model for all four kinds of Ca-alginates.The four kinds of dried Ca-alginates could be regenerated by 100 mmol L-1 HCl with 91%, 94%, 92% and 93% Cu²⁺ recovery.The mechanism of adsorption of Cu²⁺ by Ca-alginate extracted from aerobic granules was studied. The results indicated that ion exchange was the main mechanism during Cu²⁺ sorption process. In addition, the binding way of Cu²⁺ and Ca²⁺ with MG blocks was different, and the molecular conformation of alginate facilitated Cu²⁺ chelating with MG blocks at pH=4. The characteristics of heavy metal ions and stereo conformation of alginate at different pH decided the sorption characteristics of copper onto Ca-alginate.