The Performance And Mechanism Of Copper Removal In Different Induced Crystallization Systems

Water pollution caused by heavy metal effect has become a serious environmentproblem. Simultaneously the heavy metal is a widely used resource and has a veryhigh potential to reuse or recycle. In recent years, an induced crystallization-baseddisposal technology has become an international research focus, because it allows toreduce the waste production as well as to increase the recovery of materials. Asupersaturated solution formed by heavy metal ions and precipitant crystallizes coverthe surface of sand grains. Grown crystals can be recycled.The thesis compared induced crystallization processes with carbonate and sulfidein fluidized bed reactors (FBR) and discussed the effects of running conditions oninduced crystallization such as influent copper concentration, pH value, andprecipitant molar ratio. The morphologies of crystals in different systems effluentwere determined to analyze the relationship between removal efficiencies, systemmicroenvironment and product characterization. Further explore the mechanism ofinduced crystallization. Stationary running conditions: hydraulic loading15m/L,hydraulic retention time30min, reflux ratio4.29.Results of carbonate system showed: removal efficiency first increased and thendecreased as the pH in the range of6.0-10, the removal efficiency were up to98.02%when pH value was about7.0. And in the condition of pH value, the products tend tobe Cu (OH)2instead of Cu2(OH) CO3. The optimum molar rate was1.2, whichresulted in good removal efficiency and pH value of effluent kept around7.0. Withthe increase of the influent concentration, the removal efficiency was not significantlyreduced; The characteristics and morphologies of crystal products formed in theconditions of High pH (9.5), high molar ratio (3:1), high influent copper concentration(200mg/L) was uncertainty, relatively loose and poor mechanical strength.Results of sulfide system showed: removal efficiency of sulfide system increasedwith the increased of pH, the highest average removal efficiency is closer to 100%.Comparison showed that sulfide system achieved effective removal of copperions within a wider range of pH value than carbonate system, while carbonate systemwas stable faster than the sulfide system.The average fine particles production rate of reflux is3%-5%higher thanultimately effluent, which indicate reflux could capture and intercept fine particles.None of the mixed precipitation system appeared that removal efficiency of “step bystep precipitation” higher than “one step precipitation”, it means the inducedcrystallization is complex system composed of non-homogeneous nucleation andhomogeneous nucleation. When the system contains a variety of crystalline products,besides whose Ksp were close, co-crystallization phenomena were responsible for thereduction of removal efficiency.