The Removal Of Fluoride,Selenium And Arsenic From Water By Coagulation And Adsorption Using Polyalumina Compound

The inorganic polyaluminum flocculant can be devided into two kinds:one kind is“Plank-Suspending”structured polyaluminum such as P-Al₁₃ prepared by spontaneous hydrolysis;the other kind is“Core-Shell”structured polyaluminum such as K-Al₁₃ and Al₃₀ prepared by forced hydrolysis.There may be different coagulation properties between the spontaneous hydrolated product with the structure of“Plank-Suspending”and forced hydrolyzed product with the structure of“Core-Shell”.By P-Al₁₃ as the raw material,Al₅,Al₂₉ and AlOOH with diffrent alkalinity can be obtained under proper controlled conditions.All of these three kinds of aluminum compounds are insoluble.The different hydrosis-polymerization species can also lead to their different adsorption performance.Up to now,the study on the different performance of polyaluminum to removal inorganic ions?fluorine,selenium and arsenic?by coagulation and adsorption was inadequate and insufficient,which affected the further development and utilization of hydroxyl polyaluminum flocculants and polyaluminum adsorbents.In this paper,the removal of F?initial concentration:10mg/L?,different valence state Se?initial concentration 250ug/L?and different forms of As?initial concentration on 250ug/L?were studied by different structures of polyaluminum.The results indicated that P-Al₁₃ with 15 positive change has the highest removing rate,and Al₅ with an infinite network structure with the P-Al₁₃ as hydrosis has the highest adsorption performance.No matter by coagulation(by adding 0.4mmol/L P-Al₁₃)and adsorption?by adding 0.5g/L Al₅?using polyaluminium,the removal rate of fluoride ion can exceed 98%.The best method for the removal of selenium ions is adsorption method?by adding 0.5g/L Al₅,the removal rate is above 96 percent?.But the coagulation using polyaluminium is not suitable for the removal of selenium ions.The high removal rate of inorganic arensic ions can obtained by both coagulation and adsorption method.P-Al₁₃ K-Al₁₃ and Al₃₀ all had a removal rate above 96%.Only Al₅ had high removal rate,which can be above 96%with the amount of Al₅ as low as2g/L.By contrast the influence of P-Al₁₃,K-Al₁₃ and Al₃₀ on coal slurry water coagulation performance,it was founded that flocculation effect of P-Al₁₃ was better than K-Al₁₃ and Al₃₀.For the high suspended solids concentration and high turbidity coal washing water treatment,the flocculation effect of PAM+P-Al₁₃ as organic-inorganic flocculant is better than that of PAM+K-Al₁₃ and PAM+Al₃₀.they had superior flocculation effect than PAM+PAC?commercially polyaluminum chloride?.The research in this paper indicated that P-Al₁₃ and its derivative Al₅ prepared by spontaneous hydrolysis are the best polyaluminum compounds for removing inorganic ions,such as fluorine,selenium and arsenic.Its preparation method is simple,easy to control,and the raw material is easy to be obtained.It is expected to replace the K-Al₁₃ and Al₃₀ prepared by the forced hydrolysis method in water treatment.