# A Review of Adsorbents for Heavy Metal Decontamination: Growing Approach to Wastewater Treatment
## 6 Factors Affecting the Adsorption Process
### Synthetic Polymer Adsorbents
The resin showed more attraction for Cu\({}^{2+}\), Ni\({}^{2+}\) and extraction ability of metal ion was in the subsequent pattern Ni\({}^{2+}\) > Cu\({}^{2+}\) > Zn\({}^{2+}\) > Co\({}^{2+}\) > Mn\({}^{2+}\). The removal ability of metal ions by resin was decreased as the pH of the solution was decreased. [PERSON] et al. studied the sorption performance of poly (2-hydroxy ethyl methacrylate-methacrylimidophenylalanine) poly (2 HEMA-MAPA) beads [186]. The reaction of methacrylochloride with phenylalanine resulted in a metal complex comonomer MAPA. The sorption values obtained for different metals ions by the above adsorbent were 669.4 mg/g for mercury, 584.4 mg/g lead, 268.4 mg/g for cadmium, 204 mg/g for arsenic, and 115.2 mg/g for chromium. Adsorption studies and regeneration of metals suggested that poly (2-hydroxy ethyl methacrylate-methacrylimidophenylalanine) was a superior metal sorbent that had a large possibility for environmental safety. [PERSON] studied the removal of lead ions by using poly (hydroxyethyl methacrylate-N-methacryloyl-L-glutamic acid) [165]. The sorption of lead ions by the adsorbent PHEMA was insignificant (0.38 mg/g) and increased to 348 mg/g after the incorporation of the chelating group on the surface of poly 2-hydroxy ethyl methacrylate. The sorption values were found to be 42.5 mg/g for lead, 26.8 mg/g for mercury, and 17.6 mg/g for cadmium at 0.5 mol/L metal solution concentrations. Poly(acrylamide) chelating fiber was prepared by the reaction of polyacrylonitrile with hydroxylamine for extraction of copper and mercury ions as reported by [PERSON] et al. [187]. [PERSON] and [PERSON] reported a novel chelating polymer poly(acrylamide-co [1-(2-pyridylazo) 2-naphthyl-2-methacrylate(APM) having three functional moieties such as amidoxime [C(NH\({}_{2}\))=NOH)], azo(-N=N-) and carboxylic acid (-COOH) [188].The obtained polymer was able to extract trace amounts of uranium. The spectrophotometric method was used to determine U(VI) by considering arsenazo III as a complex agent. Poly(acrylamide-co {1-(2-pyridylazo) 2-nethyl-2-methacrylate (APM) resin was found to adsorb 24.2 mg of uranium per gram of resin. Poly (ethylene glycolmethacrylate-vinyl imidazole) (PEGMA-VIM) was also used for the removal of Cu2+ metal ions [189]. The maximum sorption value for metal was 30 mg of copper per gram of polymer with an initial copper metal concentration of 400 mg/L under determined optimum conditions. [PERSON] et al., prepared N\({}_{n}\)N\({}^{\prime}\)-di (carboxymethyl) dithiocarbamate) chelating resin for the removal of toxic ions from devastating streams [190]. The chelating resin prepared by reaction of N, N\({}^{\prime}\) (carboxymethyl) dithiocarbamate with chloromethylated PS-DVB matrix was used for the sorption of heavy metal ions. Poly(4-(4 vinylbenzyloxy)2-hydrobenzaldehyde P(VBH) a chelating polymer was able to remove ppb level cadmium from the aquatic system [191]. The sorption data follow up the Langmuir isotherm represented the unilayer coverage of the heavy metal on the resin surface. [PERSON] reported a new adsorbent synthesised by suspension copolymerisation method i.e., alkali blue 6B attached poly(EGDMA-HEMA) microbeads were used for the extraction of metal ions [192]. Adsorption of cadmium, copper, zinc and lead ions from the synthetic mixture of ions was studied in the concentration range 1-500 ppm at different pH values (1.5-7.5). The highest adsorption of ions onto alkali blue 6B the attached resin was 5.5 mg/g for Cd, 2.3 mg/g for Cu, 41.4 mg/g for Zn, and 125 mg/g for Pb [193]. [PERSON] et al. reported the modified polyacrylamide hydrogels synthesised by transamidation and Hofmann reactions by utilising various compounds of amine [182]. The resultant resins were utilised for the elimination of Cu\({}^{2+}\) ions at pH = 5.5 by the batch technique. The highest extraction value of resin was 2.93 mmol/g for copper obtained after a revival cycle. [PERSON] and [PERSON] reported EDTA functionalised polyacrylamide for the adsorption of metal ions.