Research And Development Of Boron Adsorbent For Seawater Desalination

Reverse osmosis seawater desalination technology is an important way to solve the shortage of fresh water resources.However,boron removal is not ideal in the current reverse osmosis desalination,and excessive boron in the fresh water is serious.Studies have shown that excessive intake of boron will harm human health,and high content of boron in the irrigation water impedes crop growth.Therefore,it is a great practical significance to research and develop a lowcost boron adsorbent with high adsorption capacity.In this paper,the boron removal characteristics of two typical boron adsorption resin?LSC-800 type,ZXC-700 type?from the market have been not only studied,but also a novel Ni?OH?₂/chitosan composite adsorbent with a high adsorption capacity has been prepared,and used to remove boron form water solutions.The main research contents and results are as follows:1.The influences of nickel chloride hexahydrate/chitosan ratio,acetic acid dosage and temperature on the adsorbent performance of the Ni?OH?₂/chitosan composite have been investigated to optimize the preparation conditions.The results show that the optimal ratio of nickel chloride hexahydrate and chitosan was 7:1,the temperature and acetic acid dosage had little effect on the preparation results.2.Static batch adsorption experiments have been carried out to investigate the effects of different contact time,pH,adsorbent dosage,temperature and initial concentration of boron on the boron adsorption from aqueous solution by LSC-800 resin,ZXC-700 resin and Ni?OH?₂/chitosan composite adsorbent,respectively.And the adsorption isotherms and kinetic charactenristics of three boron adsorbent were also analyzed.The results show that the adsorption of boron onto LSC-800 resin and LSC-700 resin were finished within 120 min,the optimum pH values were 9 and 8 respectively;Ni?OH?₂/chitosan composite adsorbent completed absorption after 4 h,and the optimum pH value was 8.The adsorption process of LSC-800 resin and ZXC-700 resin accorded with Freundlich isothermal adsorption equation,while the Ni?OH?₂/chitosan composite adsorbent accorded with Langmuir isothermal adsorption equation.Adsorption kinetics of boron onto the three adsorbent was consistent with the pseudo-second-order kinetics equation,and increasing temperature was helpful for the adsorption.3.Yoon-Nelson model and Thomas model were applied to investigate dynamic adsorption process in the column adsorption experiments.The results show that Thomas model can better describe the dynamic adsorption behavior of boron onto LSC-800 resin and ZXC-700 resin,and corresponding calculated maximum adsorption capacity of the two resins were 31.83 mg/g and29.60 mg/g,respectively;Yoon-Nelson model can better describe the behavior of boron onto Ni?OH?₂/chitosan composite adsorbent with its calculated maximum adsorption capacity of 6.87mg/g.4.The competitive ions such as Na⁺?K⁺?Ca²⁺?Mg²⁺?Cl^-andSO₄^2-in simulated seawater on boron adsorption onto LSC-800 resin,ZXC-700 resin and Ni?OH?₂/chitosan composite adsorbent have been investigated.The results show that K⁺had little effect on the boron removal of the three adsorbents,and Ca²⁺,Mg²⁺,Na⁺,Cl^-andSO₄^-2 had negative impact on the adsorbents performance.5.The adsorption capacity of the above adsorbents was almost invariable after they were used 10 times.When Ni?OH?₂/chitosan composite adsorbent is under alkaline conditions,release rate of the nickel ion is low.