Study On The Mechanism And Kinetics Of Removal Of As??? In Water By UV/TiCl₄ Photocatalytic Oxidation

Arsenic pollution in groundwater is becoming more and more serious in China,the safety of residents' living water is facing a threat.The arsenic in the groundwater is mainly in the form of trivalent inorganic?As????,and it is more toxic and difficult to remove than the pentavalent arsenic?As?V??.Removal of trivalent arsenic in water is an important subject of current research.The new titanium salt coagulation / precipitation process has attracted much attention because of its advantages of recycling products and realizing waste utilization.However,the removal efficiency of trivalent arsenic is low and the range of use is limited by the use of titanium coagulants alone.Studies have shown that UV will be As???oxidation to more easily removed As?V?,so if the introduction of UV into the coagulation process can improve the removal rate of trivalent arsenic in groundwater.In this paper,TiCl₄ was used as the coagulant and TiO₂ was used as the adsorbent.The effects of pH on the As?V?rate and the efficiency of coagulation and arsenic removal were studied.Catalyzing the oxidation of As???to As?V?and the efficiency of adsorption arsenic removal.The effects of pH value and UV irradiation on the particle size and Zeta potential of TiCl₄ hydrolyzate were also studied.The effects of pH value and UV irradiation on the particle size and Zeta potential of TiCl₄ were studied.The effects of pH value and UV irradiation on TiCl₄ coagulation.The effect of pH and UV irradiation on arsenic removal by TiO₂ adsorption,the effect of pH on the relative contribution ratio of TiCl₄ coagulation and TiO₂ adsorption to arsenic removal.The results show that the isoelectric point of TiCl₄ hydrolyzate is pH = 5.3,which is close to the isoelectric point of TiO₂ particles?pH = 5.6?.The Zeta potential of TiCl₄ and TiO₂ decreases with the increase of pH value.TiCl₄ hydrolytic sediment has the largestparticle size and the fastest sedimentation rate.The removal rate of As???by TiCl₄ and TiO₂ decreased with the increase of pH,and the removal rate of As???in TiCl₄ decreased from 70% at pH = 5 to pH = 9.The removal rate of As???from TiO₂ was reduced from 10% to 2%,and the coagulation efficiency of TiCl₄ was higher than that of TiO₂.The main mechanism of TiCl₄ removal of arsenic was coagulation and sedimentation.Under UV irradiation,The removal rate of As???decreased with the increase of pH.And the removal rate of As???was decreased from 99% at pH = 5 to35% at pH = 9,the removal rate of As???by TiO₂ from 2% at pH = 5 to 2% at pH = 9,and the increase of UV removal efficiency of TiCl₄ and TiO₂ under acidic?pH = 5-6?,UV/TiCl₄ arsenic removal mechanism is mainly coagulation sedimentation.The removal of As???is more favorable under the condition of partial acidity?pH = 5-6?and UV light.The relative contribution of TiCl₄ coagulation and TiO₂ adsorption to arsenic removal was 6: 1 at pH = 5,and the adsorption efficiency decreased with the increase of pH.The rate of As???oxidation to As?V?by UV photocatalytic TiCl₄/TiO₂ is accelerated with the increase of pH value,and the rate of As???oxidation of UV/TiO₂ is higher than that of UV/TiCl₄.UV/TiCl₄ takes As???of water to As?V?completely.The time required is T=10s,greater than UV/TiO₂.The time required for As???to be completely oxidized to As?V?is T=3-5s.In this paper,the effects of sulfate concentration on the removal of arsenic in TiCl₄ coagulation in acidic solution?pH = 5?and alkaline solution?pH = 8?were also studied.The results show that the particle size of TiCl₄ precipitates increases with the increase of sulfate concentration,and the Zeta potential decreases with the increase of sulfate concentration.The effect of sulfate concentration on the arsenic removal efficiency of TiCl₄ coagulation was higher than that of pH = 5,and the removal efficiency of As???increased from 30% to 50% with the increase of sulfate concentration.