The Absorption And Recovery Of Phosphorus With Iron-Modified Volcanic Rock Filter Media

In view of the technical requirements of deep phosphorus removal from the tail water of the sewage treatment plant,natural volcanic rock was used as raw material,which was modified by acid soaking,metal salt loading and high temperature roasting.The performance and mechanism of adsorption dephosphorization of modified volcanic rock and the recovery method of phosphorus after adsorption saturation were studied.Select the volcanic rock particles with a particle size of 3-5mm,and impregnate with HCl solution and FeCl₃ solution,then calcine in muffle furnace to produce modified volcanic rock particles.The static test results show that the modified volcanic rocks have stable adsorption capacity in the range of 5.0-9.0 pH value,and the influence of temperature on the adsorption performance of modified volcanic rocks is not obvious in the range of 5-35℃.The simulation of Webber-Morris model shows that the adsorption reaction of volcanic rocks is not completely controlled by the diffusion process in particles,but the result of several processes.The fitting results of isotherm adsorption curve show that Langmuir model can better describe the process of phosphorus removal by adsorption of volcanic rocks.HCl solution with the concentration of 1.0mol/L has a good analytical effect on volcanic rocks.XRD,XRF,SEM and FTIR were used to characterize the physical and chemical properties of volcanic rocks in different stages.The results show that the elements of the volcanic rocks are mainly composed of Si,Fe and Ca,and the content of Fe increases by 3.5% after modification.The crystal structure of the volcanic rocks before and after modification has no obvious change,and the main crystal composition is FeCl₃.In the process of modification,after calcination at high temperature,FeCl₃ loaded on the surface of volcanic rocks is oxidized to Fe₂O₃.In the process of adsorption of phosphate in water by volcanic rocks,the main reaction are the ion exchange reaction between Fe-OH bond and phosphate and the chemical precipitation reaction between Fe₂O₃ and phosphate.After the desorption,the amount of Fe₂O₃ loaded on the surface of volcanic rock decreased,and the morphology changed.The results of dynamic test of adsorption column show that the volcanic rocks have the priority of phosphorus adsorption,and also have certain adsorption capacity for ammonia nitrogen and other substances.After the adsorption is saturated,the desorption is carried out with a concentration of 1.00mol/L HCl solution.After the first desorption,the adsorption cycle of the adsorption column is reduced from 120h to 75h.Then repeated desorption reabsorption steps,the adsorption cycle of the adsorption column changed little and the adsorption effect was relatively stable.Struvite crystallization is better than calcium phosphate crystallization in the phosphorus recovery of desorption solution.After the adsorption column is saturated,the HCl solution with a concentration of 1.00mol/L is used for desorption.According to the ratio of n(Mg²⁺):n(PO₄^3-):n（NH₄⁺）=1.5:1:1,MgCl₂ and NH₄Cl are added into the desorption solution at the same time,the TP removal rate is 78.1%,and the purity of guanosine is 80.5%.