Preparation Of Modified Crab Shells Adsorbent And The Adsorption Capacity Of As(?)in Water

Arsenic contamination of water has become a major public health problem in many countries,and about 150 million people is affected in worldwide.At present,the common methods of arsenic removal mainly include oxidation,coagulation and sedimentation,ion exchange,membrane separation,adsorption and so on.Compared with other methods,adsorption is simple,renewable and selective.It is especially suitable for large water treatment system with low arsenic concentration.In recent years,the research and development of waste biological materials has attacted wide attention in the field of arsenic removal.The source of these materials is very extensive and the arsenic removal can be improved by chemical modification.These materials has great potential in the field of water treatment.In this study,aluminum/lanthanum/crab shell particle adsorbent?Al-La-CS?and aluminum/cerium/crab shell particle adsorbent?Al-Ce-CS?were prepared by impregnation method using waste crab shell?WCS?,aluminum chloride?Al Cl₃?,lanthanum chloride?La Cl₃?and cerium nitrate?Ce?NO₃?₃?.The influence of four factors,such as the molar ratio of metal to metal,the particle size of the material,the modification time and the modified temperature,on the removal of arsenic was studied.The optimum preparation conditions of Al-La-CS and Al-Ce-CS system were obtained.The materials were characterized by FTIR,SEM-EDS,XPS,BET,and Zeta potentials.The effects of dosing amount,initial p H value,initial As???concentration and coexisting anion on the adsorption effect were studied by static experiment.In addition,the adsorption isotherm and adsorption kinetics were investigated.The results are as follows:?1?The optimum preparation conditions of Al-La-CS system were as follows:the molar ratio of Al and La was 1:0.5,particle size was 60 mesh,the modified time was 4h,and the modification temperature was 40?.The optimum preparation conditions of Al-Ce-CS system were as follows:the molar ratio of Al and Ce was 1:0.5,particle size was 60 mesh,the modified time was 4h,and the modified temperature was 60?.?2?The specific surface area and pore volume of Al-La-CS and Al-Ce-CS are higher than those of WCS.FTIR,EDS and XPS show the Al and La have been successfully loaded on Al-La-CS surface and Al and Ce have been successfully loaded on Al-Ce-CS surface,which lead to a sharp increase in the positive charge of the surface and is helpful for the As???adsorption.?3?The removal of As???by Al-La-CS was significantly higher than that of WCS.When Al-La-CS increased from 0.1 g/L to 2.0 g/L,As???removal increased from 30.6%to 93.6%.When the dosage further increased to 6.0 g/L.the As???removal was about 95%and remained constant.At p H 2,the As???removal is about 39%.At p H>9,the the As???removal is blow50%.And at p H 3-9,the As???removal is above 90%.When the initial As???concentration increased from 0.1 mg/L to 200 mg/L,the adsorption capacity of Al-La-CS increased gradually to 65.25 mg/g.When the initial concentration continued to increase to 400 mg/L,the adsorption capacity is almost constant.At the same concentration,the effect of the anions on the arsenic removal was Si O₃^2->PO₄^3->HCO₃^->NO₃^->Cl^-.Langmuir isotherm model can well describe the adsorption of on As???by Al-La-CS.At 20?,30?and 40?,the maximum adsorption capacity of the Langmuir adsorption isotherm was 57.670,63.171,74.627 mg/g,respectively,which was similar to the experimental results.?4?The As???removal using Al-Ce-CS was significantly higher than that of WCS.When Al-Ce-CS increased from 0.1 g/L to 2.0 g/L,As???removal increased from 35.7%to 96.1%.When the dosage further increased to 6.0 g/L.the As???removal was about 98%and remained constant.At p H 2,the As???removal is about 30%.At p H>9,the the As???removal is blow60%.And at p H 3-9,the As???removal is above 95%.When the initial As???concentration increased from 0.1 mg/L to 300 mg/L,the adsorption capacity of Al-La-CS increased gradually to 68.17 mg/g.When the initial concentration continued to increase to 400 mg/L,the adsorption capacity is almost constant.At the same concentration,Cl^-has little effect on arsenic removal,while the effect of Si O₃^2-,PO₄^3-,HCO₃^-and NO₃^-on the arsenic removal is relatively large.Si O₃^2-and PO₄^3-can obviously inhibit the As???adsorption.Langmuir isotherm model can well describe the As???adsorption by Al-Ce-CS.At 20?,30?and 40?,the maximum adsorption capacity obtained by the Langmuir adsorption isotherm equation is 57.571,63.171,75.019 mg/g,which is close to the experimental results.