Asparagus Potamogeton Modification Of Adsorption Characteristics Of Heavy Metals

Biosorption is a new potential technology to treat wastewater containing heavy metal.The main object of this study is to develop a new biosorbent which is low cost and high efficiency.Potamogeton pectinatus L.,a submersed aquatic macrophyte,was selected as raw material for biosorbent based field investigation,sampling analysis and comparison with other low cost absorbent.Batch experiments were conducted to evaluate the adsorption of copper ions in aqueous solution using P. pectinatus L.directly.Two kinds of modification method were used to change the chemical property of P.pectinatus L.and the better one was adopted.Several important factors in the modification process were investigated,optimum modification conditions were achieved through orthogonal test.Modification and adsorption mechanisms were discussed by means of modern analysis methods of FT-IR,SEM,EDS,ICP-AES. The adsorption properties of modified P.pectinatus L.to some heavy metal ions such as Cu²⁺,Pb²⁺,Zn²⁺ and Cd²⁺ were measured by static method.In addition,desorption experiments and regeneration test were carried out to discuss the recycling feasibility of the biosorbent.The following conclusions were drawn:(1) P.pectinatus L.has great adsorption potential for Cu²⁺ from wastewater,but there are several problems such as the equilibrium time is long,the adsorption capacity is small and organic concentration in solution is high after adsorption when P.pectinatus L.is used directly as adsorbent.(2) The Cu²⁺ adsorption properties of Potamogeton pectinatus L. was highly improved after modification using methyl alcohol.The adsorption kinetic was well-fitted with pseudo-second-order sorption equation and the adsorption isotherms followed the Langmuir model.The Cu²⁺ adsorption onto modified Potamogeton pectinatus L.mainly relied on the Complexation of Cu²⁺ and O-H group which existed in alcohols and phenols,the groups of C=O,N-H and C-N in amides,S=O group in Sulfones.(3) The modification effect using NaCl solution is better than that of methyl alcohol.The optimized modification conditions are following: concentration of NaCl solution is 0.75 mol/L,modification time is 8 h and the ratio of absorbent to modifier is 1:75.The Cu²⁺ adsorption rate was highly increased after modification using NaCl,for adsorption sites on cell walls were adequately exposed and massive Na⁺ loaded to the surface of adsorbent,which improved the ion exchange capacity of the adsorbent.(4) The equilibrium of the adsorption process of heavy metal ions onto NaCl-modified Potamogeton pectinatus L.can be attained within 30min,and the optimum initial pH rang is 3～6.The maximum adsorption capacities of Cu²⁺,Pb²⁺,Zn²⁺ and Cd²⁺ are 36.20 mg/g,124.24 mg/g,39.42 mg/g and 62.76 mg/g respectively.The competitive powers of various metal ions are in the order of Pb²⁺＞Cu²⁺＞Cd²⁺＞Zn²⁺. The initial concentrations of simulated wastewater for Cu²⁺,Pb²⁺,Zn²⁺ and Cd²⁺ are 202.1±3.99mg/L,408.6±4.75 mg/L,203.0±5.50 mg/L,203.0±5.50 mg/L respectively,and the residual concentrations of each metal ions can meet the Integrated Wastewater Discharge Standard(GB 8978-1996) after three-stage adsorption.(5) Recycling utilization of the biosorbent can be realized after being desorbed with hydrochloric acid of 0.06 mol/L and then regenerated with sodium bicarbonate of 0.05～0.5 mol/L.