Cd(Ⅱ)speciation in fresh and mine drainage waters has been calculated using a thermodynamics approach using Cd(Ⅱ)concentrations,ligand concentrations,pH and ionic strength as inpur parameters.Consequently,crosslinked chitosan(CCS)microspheres tethered with pH-sensitive poly(methacrylic acid)(PMAA)brushes were developed for the efficient removal of Cd(Ⅱ)ions from aqueous solutions.Functional PMAA brushes containing dense and active carboxyl groups(-COOH)were grafted onto the CCS microsphere surface via surface-initiated atom transfer radical polymerization(ATRP).Each functionalization step was ascertained by Fourier transform infrared(FTIR),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM)and water contact angle measurements.Batch adsorption results showed that solution pH values had a major impact on cadmium adsorption by the PMAA-grafted CCS microspheres with optimal removal observed above pH 5.The PMAA-grafted CCS microspheres were found to have a significantly larger adsorption capacities and faster adsorption kinetics for Cd(Ⅱ)ions than the CCS microspheres.The adsorption equilibrium of Cd(Ⅱ)was achieved within 1 h on the CCS-g-PMAA microspheres,much faster than about 7 h on the CCS microsphere.At pH 5 and with initial concentration of 0.089-1.3 mM,the maximum adsorption capacity of Cd(Ⅱ),derived from the Langmuir fitting,on the PMAA-grafted CCS microspheres was around 1.3 mmol/g.Desorption and adsorption cycle experimental results demonstrated that the Cd(Ⅱ)loaded on the PMAA–grafted CCS microspheres can be effectively regenerated in diluted HNO3 solution,and the adsorption capacity remained almost unchanged upon five-cycled reuse.