Removal Of Arsenite And Arsenate By Basic Yttrium Carbonate In Fixed-bed Column

Arsenic（As）is an element widely distributed in nature,and it mainly exists in the environment in the forms of As（Ⅲ）and As（Ⅴ）.Both As（Ⅲ）and As（Ⅴ）have a high toxicity that they have been identified as the first class of carcinogens by the International Cancer Research Center.Because arsenic’s unique physical and chemical properties,arsenic and its compounds are widely used in pesticides,fertilizers,wood preservatives and semiconductor industry and other fields.As a result,a lot of waste water containing arsenic in the production and application processes of these industries causes serious arsenic contamination problems.Adsorption method has become one of the most effective methods of arsenic removal owing to the advantages of convenience,high efficiency and low-cost.In recent years,new adsorbents based on rare earth elements have earned widespread concern at home and abroad,and basic yttrium carbonate（BYC）is one of them.BYC has the characteristics of simple synthesis,high adsorption capacity,easy recycling,etc.,which has a great advantage in terms of arsenic adsorption.In view of the continuity and mobility of practical application,dynamic adsorption is more practical.In this paper,dynamic adsorption was used in As（Ⅲ）and As（Ⅴ）removal by BYC.The main contents were as follows:At room temperature,the effects of pH,initial As（Ⅲ）concentration,adsorbent dosage,flow rate,competing anions were investigated on the dynamic adsorption of As（Ⅲ）by BYC.In conjunction with the effluent pH and FTIR spectra,the mechanism of adsorption was explored.The results showed that the effect of solution pH on the dynamic adsorption of As（Ⅲ）by BYC was very weak.With the increase of initial As（Ⅲ）concentration,the adsorption rate was increased,and the adsorption capacity was greater.The adsorption rate was increased when decreasing adsorbent dosage or increasing flow rate.PO43-and CO32-had a significant competitive effect on As（Ⅲ）adsorption,followed by SO₄^2-,and NO₃^-hardly affected adsorption.Under the experimental conditions of solution pH 6.0,50 mg/L of initial As（Ⅲ）concentration,0.1 g of BYC dosage and 1.0 mL/min of flow rate,the adsorption capacity of As（Ⅲ）was 89.38 mg/g at 480 min.Meanwhile,the results indicated that As（Ⅲ）adsorption belonged to specific adsorption by measuring the effluent pH and the characterization of adsorbent before and after adsorption,mainly forming inner-sphere complexes between surface Y-OH and As（Ⅲ）.In addition,the observation showed that the replacement of CO32-was also involved in the arsenite uptake.The breakthrough curve of As（Ⅲ）effluent can be analyzed well by Yoon-Nelson model.The effects of pH,initial As（Ⅴ）concentration,adsorbent dosage,flow rate,competing anions were also studied on the dynamic adsorption of As（Ⅴ）by BYC at room temperature.The results showed that the adsorption of As（Ⅴ）by BYC was significantly higher than As（Ⅲ）adsorption.Under the experimental conditions of solution pH 6.0,100 mg/L of initial As（Ⅴ）concentration,0.1 g of BYC dosage and 1.0 mL/min of flow rate,the adsorption capacity of As（Ⅴ）could reach up to 279.51 mg/g at 480 min.As（Ⅴ）adsorption was highly pH-dependent,and this phenomenon implied that electrostatic attraction should play an important role in As（Ⅴ）adsorption.With As（Ⅴ）concentration increasing or adsorbent dosage decreasing or flow rate increasing,the adsorption rate increased.Only PO43-had strongly competing effect on arsenate removal,and other oxyanions barely influenced As（Ⅴ）adsorption.Combining the determination of the effluent pH and CO32-concentration with the characterization of sorbent,it was found that As（V）not only formed inner-sphere complexes with surface Y-OH,but also exchanged with CO32-.In addition,the precipitation of H2AsO4-and Y3+ also took place in As（Ⅴ）uptake under acidic conditions.Perhaps,it was the reason why BYC had a great removal capacity of As（Ⅴ）in acidic conditions.