Study On Application Of Poly(Acrylic-co-Acrylamide) Hydrogel In Wastewater Treatment

With the rapid development of modern industry, the environmental problems are becoming more and more serious. The growth and reproduction of plants and animals, human health and living environment have been severely threatened from the pollution of heavy metal and organic dyes. Therefore, it is important to establish an efficient, environmental friendly and low-cost method for the treatment of heavy metal ions and dyes wastewater. As a new polymer materials with three-dimensional network structure, hydrogel is able to perceive and give response for the stimulation of environmental change, and can be added into different chelating groups, with its great water permeability, biological compatibility and degradation,so it has been widely used in industry, agriculture, forestry, horticulture, biomedicine,pharmacy and other fields. As a new type of environmental adsorption material, hydrogel provides a new way to solve the problem of heavy metal ions and organic dyes in water. The preparation methods and adsorption properties of acrylic acid acrylamide hydrogels have been widely concerned, but the effect of environmental factors on the adsorption properties of the hydrogel is still lack of systematic research.Using acrylic acid and acrylamide as monomer, potassium persulfate and N,N’-methylenebisacrylamide as initiator and crosslinker, the P(AA-co-AM) hydrogel was prepared by aqueous polymerization and optimized through orthogonal test. P(AA-co-AM)hydrogel was characterized by means of FTIR, SEM and XPS. The adsorption isotherm,kinetic and thermodynamic behavior of heavy metal ions and dyes on P(AA-co-AM) hydrogel were discussed. And the effects of the synthesis condition, particle size, temperature, p H value,interfering ions, competitive adsorption, and initial concentration of heavy metal ions and dyes in solution on the swelling property and adsorption capacity were investigated. The study shows that:The results of FTIR, SEM and XPS experiments indicate that the P(AA-co-AM) hydrogel has three-dimensional network structure with carboxyl and acylamino. The carboxyl and acylamino can efficiently interact with heavy metal ions(Cu2+, Pb2+, Zn2+, Cd2+) and dyes(ST,CV, MB, MG) to form chelates.In terms of P(AA-co-AM) hydrogel for adsorbing heavy metal ions, as n(AA/AM) was 5,neutralization degree was 80%, initiator and crosslinker amount were 2% and 0.8%, it reached the maximum adsorption capacity of heavy metal ions. In terms of P(AA-co-AM) hydrogel for adsorbing dyes, as n(AA/AM) was 2, neutralization degree was 70%, initiator and crosslinker amount were 0.6% and 0.8%, it reached the maximum adsorption capacity ofdyes.In the scope as we concerned, as n(AA/AM) was 2.5, neutralization degree was 70%, initiator amount was 0.4%, crosslinker amount was 0.8%, the P(AA-co-AM) hydrogel had the maximum swelling degree in ultrapure water. The increase of the swelling temperature and p H value could promote the adsorption reaction. After swelling 8h, the equilibrium was reached. Swelling degree of P(AA-co-AM) hydrogel would have obvious decrease with the increase of concentration of the solution with Na+, heavy metal ions and dyes.The decrease of the particle size of the P(AA-co-AM) hydrogel, and the increase of the p H value of heavy metal ions solution and adsorption temperature could positively influence the adsorption reaction, which was an endothermic process. The maximum absorption amount of Cu2+, Pb2+, Zn2+ and Cd2+ were 185.73, 587.99, 208.42 and 402.86 mg·g-1, which was obtained by using absorbent with particle size of 100~160 mesh, under 35 ℃ and p H value of5. The adsorption kinetic followed the pseudo-second-order kinetic mode(R2>0.98), the result of particle diffusion model was better than liquid film, and the adsorption isotherm fit the Langmuir equation(RL>0.95).The interfering ions experiment showed that the P(AA-co-AM)hydrogel has good selective adsorption for Pb2+. After desorption of 3 times by EDTA-2Na,the desorption rate of the P(AA-co-AM) hydrogel could still reach above 80%.The decrease of the particle size of the P(AA-co-AM) hydrogel, and the increase of the p H value of dyes solution could positively influence the adsorption reaction. And increasing the adsorption temperature could promote the adsorption reaction of ST, CV, and MG, but inhibit the adsorption reaction of MB. The maximum absorption amount of ST, CV, MB and MG were 599.56, 620.45, 602.72 and 575.01 mg·g-1, which was obtained by using absorbent with particle size of 60~100 mesh, under 35 ℃ and p H value of 5. The adsorption kinetic followed the pseudo-second-order kinetic mode(R2>0.99), the reaction before saturation followed the particle diffusion model. And the adsorption isotherm fit the Freundlich equation(RF>0.97).After desorption of 3 times by HCl, the desorption rate of P(AA-co-AM)-ST and P(AA-co-AM)-MB were 82.93%, 75.35%, 66.26% and 78.18%, 68.35%, 59.34%. The COD,TOC, TN of ST and MB solution could have obvious decrease after adsorption by the P(AA-co-AM) hydrogel.