Preparation Of The Spherical ZrO（OH）₂/AlOOH Composite And Its Sulfate Radical Adsorption Performances

Sulfate ions widely exist in domestic wastewater,industrial wastewater and process circulating water.Excessive concentration of SO₄^2-will corrode and damage equipments and endanger human health.By comparing the effects of sulfate removal methods,the adsorption method of zirconium-based materials has advantages of high selectivity,low cost and so on.However,the adsorbent of hydrate zirconia is still used in the form of powder,forming a slurry bed in the adsorption-desorption operation,so it is hard to regenerate and separate adsorbents from brine or wastewater,thus reducing efficiency and increasing costs.Therefore,it is significant to explore that granular zirconium adsorbents are applied to industrial water treatment.In this work,spherical composites with large specific surface area and high adsorption properties were prepared by adopting a sol-gel method.The micromorphology,crystal and pore structure of adsorbent were analyzed,and the component and formation mechanism of composites were discussed.The static and dynamic adsorption-desorption properties of adsorbents were investigated,and the effects of different adsorption conditions（adsorption time,temperature,solution concentration and flow rate,etc.）on the adsorption properties of composites were explored.Combining with the dissolution of adsorbents,the best static and dynamic adsorption conditions were determined,and the desorption-regeneration performance of the adsorbent was estimated with Na OH solution.The composites before and after adsorption were characterized,and the mechanism of adsorption desorption was investigated.The results indicated that the spherical adsorbent is an amorphous nanocomposite.Due to the continuous dehydration and condensation of hydroxyl groups on the surface of colloidal particles,the adsorbent has a uniform nanoflake structure with a thickness of about 10-30 nm;and the nanoflake is composed of nano strip-like or rod-like particles,the diameters of which are below 5 nm.The adsorbent is a typical mesoporous material with a high porosity（6.23 nm）and specific surface area（220.22 m²/g）.The static adsorption data of composites were consistent with Langmuir isotherm equation and pseudo second-order equation,indicating that SO₄^2-adsorbed on the surface of adsorbent was a uniform monolayer adsorption,and the adsorption process was chemisorption.Thermodynamic studies showed that the adsorption of sulfate was spontaneous and exothermic.The optimum static adsorption conditions:adsorbent with Zr/Al molar ratio of 0.2,solution p H was 2,continuous adsorption at room temperature for 150 minutes,the maximum adsorption capacity with 14 g/L SO₄^2-solution was 205 mg/g.The desorption experiment with 25 g/L Na OH solution demonstrated that the good regeneration performance of adsorbent.The adsorbents have good sphericity and mechanical strength.In the study of dynamic adsorption,decreasing the concentration and flow rate of SO₄^2-solution and increasing the height of the bed properly can effectively improve the utilization of adsorbing column.The optimum dynamic adsorption conditions:the initial concentration of SO₄^2-solution was 1-2 g/L,the solution p H was 2,the flow rate was about 1.5 m L/min,the bed height of the adsorbent was about 10 cm,and the saturated adsorption capacity of the column was 108.22 mg/g,the Na OH solution of 5-10 g/L was used for desorption and regeneration.The adsorption-desorption mechanism indicated that the active component Zr-OH on the surface of the adsorbent participated in the adsorption of SO₄^2-,the composites adsorbed SO₄^2-in acidic solution and desorbed in alkaline solution by ion exchange.