Technical Study On Treatment Of High Concentration Calcium-containing Wastewater Using Simulated Moving Bed

The high concentration of calcium in the water will increase the water hardness,which has a negative effect on domestic water,but also directly affect the equipments serve life and the normal utilization of facilities.Therefore,a high-efficiency method for the removing of calcium is meaningful and has important guiding significance.In this paper,the simulated moving bed technology(SMB)were used to treat the calcium-containing wastewater for the calcium mass concentration of 2000 mg/L,with the natural clinoptilolite as ion exchanger,the sodium sulfate solution as regenerating agent.Firstly,the clinoptilolite were modified to Na-pretreated zeolite through the sodium chloride solution,which increased the adsorption capacity of calcium.Thermodynamics experiment and kinetics were carried out.The results showed that the thermodynamic data were more fitted to Langmuir isotherm model,which is a spontaneous and entropy increaseendothermic reaction process while adsorption kinetics data preferably followed the pseudo-second-order model and the adsorption rate was mainly controlled by the liquid film diffusion.Secondly,the temperature,inlet flow rate and initial concentration of calcium were investigated as the influencing factors.Meanwhile,the relationship between height of mass transfer zone and inlet rate was obtained by 5 zeolite columns in series for the adsorption zone.The outcomes showed that lower flow rate and higher temperature were benefit to the adsorption capacity.The optimum condition for the height of mass transfer zone was about 3.9 m with the inlet flow rate of 12 m/h.For the regeneration experiments,the different regeneration temperature and regeneration agent concentration,as well as the regenerant into the liquid flow rate conditions were considered as influence factors,the regeneration of zeolite column curves showed the lower flowed rate,higher temperature and higher regenerant concentration were helpful.Van-Deemter equation illustrated the best liquid velocity for regeneration zone which is 4.87 m/h.Finally,for the simulated moving bed continuous experiment,we conclude that the best number of column for simulated moving bed system was 5;the switching time was 80 min and operation temperature was 90 °C;Adsorption zone should use 2 columns in series and liquid velocity with 12 m/h;Regeneration zone should use 3 columns in series and regenerant concentration with 15 % and liquid velocity with 4 m/h.When the operation is stable,the concentration of calcium in the outflow of adsorption zone is lower than 8 mg/L,calcium removal rate was above 99.6 %,and average calcium concentration in the regenerative liquid was about 6.3 g/L.