Adsorption Characteristics Of Calcium In Seawater

With the development of seawater desalination technologies,how to deal with the brine is becoming more and more important.A lot of calcium ion was in brine.The high calcium concentrations are problematic,because they result in clogging of pipelines and heat exchangers through scaling as the form of carbonate precipitates et al.Therefore the removal of calcium plays a very important role in utilization of brine.Zeolite is getting more and more attention because its adsorption capacity and the characteristics of good selectivity.Ca-Selectivity zeolite sample was prepared.The structure morphology,the physical and chemical performances were characterized by SEM,XRD and FT-IR.The adsorptive experiments were carried out in batch systems.The models were adopted to evaluate the experimental data.The Langmuir,Freundlich isotherms were adopted to evaluate the experimental data in fixed-pH.Three different kinetic models including pseudo-first-order model,pseudo-second-order model and intra-particle diffusion model were used to evaluate the adsorption kinetics and the competitive adsorption models were fitted to data in the condition which the pH values are without any control during adsorption process,time dependence study and mechanism was studied at different pH.Within the test range(initial concentration 200～1000 mg/L,sorption dose 0.1～0.7 g,pH 2～12.5,contact time 0～100min,tempreture 298K～318K),sorption performance for calcium ions showed an increase metal uptake capacity with an increasing in initial ions concentration and an increasing in tempreture but an decreasing in sorbent dose.The optimized condition of pH value for calcium is 12.5,while contact time is about 70 min.At equilibrium, the maximum total uptake by Ca-Selectivity zeolite was 105 mg/g.The results for calcium fit well to the Langmuir.Pseudo-second-order model described the sorption kinetic of calcium well.The Model assumes direct competition between metal and H~+ ions for binding sites and has been shown to fit the experimental data well.It is an endothermic process accompaning the increase of disorder of the system and can be occured spontaneously.From the effect of ionic strength and the sorption in simulated sea water,it can be seen that the adsorption amount of calcium decreased with the increase of TDS,but the Ca-Selectivity zeolite still exhibited high calcium ion exchange capability,we can conclude that the Ca-Selectivity zeolite was a potential adsorbent for calcium removal from brine.