5. Biopolymer Chitosan Membranes Prepared from Fishery Waste for the Removal of Zinc Ions from Aqueous Systems by Adsorption

Chitosan was derived from the Cape rock crab outer shell, as seen in the areas of Cape Town, South Africa, and was exploited in the manufacture chitosan particles employed in the development of porous polymer chitosan membranes through a step reversal procedure. The chitosan membrane was cross-linked with 2.5% glutaraldehyde; chitosan membrane (CS) and cross-linked chitosan membrane (XCS) were characterize by FTIR, XRD, SEM-EDX and TGA. Equilibrium findings showed that the Langmuir equilibrium model can be appropriately applied in explaining zinc adsorption on XCS and the maximum adsorption potential for temperatures between 303 and 313 K was 2.64 mmol g⁻¹. The adsorption operation was discovered to be endothermic, with 20 kJ mol⁻¹ adsorption enthalpy. Flux via XCS is a mechanical mechanism with a decline in the adsorption rate (1.91–1.30 mmol g⁻¹) as the flux rises (2–55 L m⁻² hr⁻¹). XCS adsorption of metal ions has also been noticed to be impacted by co-ions, where the influence of nitrates has been considered to restrict adsorption, whereas sulphates have been proven to raise adsorption. The regeneration of the adsorbed zinc ions was accomplished employing sulphuric acid and hydrochloric acid solutions as eluants. The former was considered to be a more powerful eluant. As a result, a sulphuric acid solution with a pH of 2 can retrieve up to 90% of the adsorbed zinc. Consequently, upon recovery, the adsorption capacity was observed to be lowered. Upon regeneration, this decline in adsorption efficiency may be due to membrane mass loss of approximately 11%. The functional stability of the membrane was compromised following two regeneration periods, and the membranes were no longer functional.