# A Review of Adsorbents for Heavy Metal Decontamination: Growing Approach to Wastewater Treatment
## 6 Factors Affecting the Adsorption Process
### Synthetic Polymer Adsorbents
This membrane easily removed the heavy metal ions i.e., Cu(II), Ni(II), Pb(II), Zn(II), and Cd(II) from their synthetic solutions. The concentrations of these five heavy metal ions in the resulting solution were 1.0 g/L, 2.0 g/L, and 5.0 g/L, respectively. The removal of heavy metal ions by forwarding osmosis (FO) membranes was influenced by the pH of the synthetic solution, time, temperature, regeneration as well as concentration. [PERSON] and co-workers synthesised permeable adsorbents of ZII-8 and ZII-67 and used them for the extraction of Pb\({}^{2+}\), Cu\({}^{2+}\) from wastewater [87]. [PERSON] et al. studied the extractions of nickel ions from contaminated solutions by ultrafiltration membranes of natural chitosan or synthetic carboxymethyl cellulose through electrostatic interactions [221]. Here, both cellulose and carboxymethyl cellulose were mixed together for one hour at room temperature to obtain complete dissolution. The concentration of nickel ions ranged from 1 to 100 ppm corresponding to molar concentrations from 1.7 \(\times\) 10\({}^{-5}\) to 1.7 \(\times\) 10\({}^{-2}\) mol/L. Above mentioned, two polymers have the same removal tendency at neutral pH value; however, chitosan has proved outstanding elimination performances in basic conditions (above its pKa), whereas carboxymethyl cellulose has shown poor removal capacity at pH (3.5-4.0). However, CMC would be preferred to chitosan in natural conditions (4 < pH < 8) since its effect on the permeation flux was less important. Lignin xanthate resin (LXR) was prepared by a two-step process from alkaline lignin and CS\({}_{2}\). According to the Langmuir model, the maximum amount adsorbed by this resin was 64.9 mg/g for lead ions at 30 \({}^{\mathrm{o}}\)C. Adsorption of lead ions by lignin xanthate resin (LXR) was more effective for lead ions than alkaline lignin due to the xanthate group. The adsorption capacity of lead ions was increased steadily to 62.5 mg/g with increasing pH from 1.0 to 5.0. The adsorption of Pb\({}_{2+}\) on LXR achieved equilibrium within 90 min [222]. [PERSON] and co-workers reported the nanoparticle-containing cellulose for the removal of heavy metal ions. Cellulose was impregnated with silver and zinc oxide nanoparticles by using the co-precipitation method [223]. It was found from the batch method that the adsorption of metal ions on zinc and silver NPs impregnated cellulose was very rapid and achieve equilibrium within 30 min. The cellullose impregnated zinc and silver composites adsorbents showed excellent metal affinity in the order of Hg\({}^{2+}\) > Ni\({}^{2+}\) > Cr\({}^{3+}\) > Co\({}^{2+}\). Adsorption capacities of cellulose impregnated with silver and zinc oxide nanoparticles was found to be Hg\({}^{2+}\) = 104.6 mg/g, Cr\({}^{3+}\) = 56.52 mg/g, Co\({}^{2+}\) = 45.33, Ni\({}^{2+}\) = 61.48 mg/g, Pb\({}^{2+}\) = 37.21 mg/g and Hg = 789.3 mg/g, Cr\({}^{3+}\) = 266.3 mg/g, Co\({}^{2+}\) = 245.1 mg/g, Ni\({}^{2+}\) = 222.9 mg/g, Pb = 92.22 mg/g for 1.0 g of sorbent amount. For 0.5 g sorbent amount of ZnC, adsorption capacities were 107.8 for Hg\({}^{2+}\), 83.02 for Cr\({}^{3+}\), 50.44 for Co\({}^{2+}\), 43.81 for Pb\({}^{2+}\) and 101.2 mg/g for Ni\({}^{2+}\) ion. For 0.5 g adsorbent dose of AgCt, adsorption capacities were 554.5 mg per gram for mercury, 157.75 mg/g for chromium, 114.1 for cobalt, 84.595 mg/g for lead, and 204.935 mg per gram for nickel ions calculated according to Langmuir adsorption isotherm. [PERSON] et al. synthesised a porous jute/polyacrylic acid gel by using free-radical polymerisation of acrylic acid in jute aqueous solution [224]. The Jute/PAA gel sorbent could proficiently extract particularly cadmium and lead toxic metal present in industrial effluent. Adsorption capacities of the jute/PAA gel sorbent were 401.7 mg/g for cadmium and 542.9 mg/g for lead toxic metal ions. Additionally, the sorption equilibrium achieved within ten minutes for 40 ppm of cadmium and lead by using 1.0 g/L sorbent.