The present study reported synthesis of a new inorganic exchanger, i.e., zirconium hydrogen monothiophosphate [Zr(HPO3S)2, denoted ZrPS] and its selective sorption toward Pb(II), Cd(II) and Zn(II) ions. ZrPS sorption toward all the three metals is dependent upon solution pH due to the ion-exchange nature. As compared to another inorganic exchanger zirconium phosphate [Zr(HPO4)2, denoted ZrP], ZrPS exhibits highly selective sorption toward these toxic metals from the background of calcium ions at great levels. Such sorption preference is mainly attributed to the presence of-SH group in ZrPS, as further demonstrated by FT-IR analysis and XPS study. Moreover, ZrPS particles preloaded with heavy metals could be efficiently regenerated with 6M HCl for multiple use without any noticeable capacity loss. All the experimental results indicated that ZrPS is a promising sorbent for enhanced heavy metals removal from contaminated water.

Adsorption is one of the most widely applied techniques for environmental remediation. Its kinetics are of great significance to evaluate the performance of a given adsorbent and gain insight into the underlying mechanisms. There are lots of references available concerning adsorption kinetics, and several mathematic models have been developed to describe adsorption reaction and diffusion processes. However, these models were frequently employed to fit the kinetic data in an unsuitable or improper manner. This is mainly because the boundary conditions of the associated models were, to a considerable extent, ignored for data modeling. Here we reviewed several widely-used adsorption kinetic models and paid more attention to their boundary conditions. We believe that the review is of certain significance and improvement for adsorption kinetic modeling.

Aminated polystyrene resins (NDA-101 and NDA-103) were synthesized, and their adsorption performances for phenol in aqueous solutionwere investigated and compared with the commercial polystyrene resin (Amberlite XAD-4) andweakly basic polystyrene resin (Amberlite IRA-96). All the associated adsorption isotherms are well described by Freundlich and Langmuir equations. The results indicated that all the four resins spontaneously adsorb phenol driven mainly by enthalpy change, and their adsorption capacities, free energy changes, enthalpy changes, and entropy changes for phenol followed the same order as: NDA-101>NDA-103>XAD-4>IRA-96. Surface energy heterogeneity analysis by Do's model also suggested that the surfaces of XAD-4 and IRA-96 were more homogeneous, and the better adsorption capacity and affinity of the aminated resins (NDA-101 and NDA-103) are probably due to their multiple hydrogen bonding and-stacking interactions with phenol molecule.

Removal and recovery of aromatic pollutants from water by solid adsorbents have been of considerable concern recently. Relatively limited information is available on desorption kinetics and isotherms aspects. In the present study, batch desorption experiments of loaded 4-nitrophenol on a hyper-cross-linked polymer resin NDA-701, a polymeric adsorbent Amberlite XAD-4 and a granular activated carbon GAC-1 were carried out to study the effects of reaction temperature and pore-size distribution of adsorbents. 4-Nitrophenol desorbed rapidly in the early stages, followed by a much slower release, whichwas described well by a first-order two-component four-parameter model. The adsorption and desorption equilibrium isotherms were well described by Freundlich equation and the apparent adsorption-desorption hysteresis (hysteresis index) for 4-nitrophenol followed an order as: NDA-701≈XAD-4 GAC-1. Analysis of adsorption-desorption process suggested that higher reaction temperature and larger proportion of macropore of adsorbents favoured desorption kinetic and reduced adsorption-desorption hysteresis. All the results indicated that NDA-701, with a specific bimodal property in macro-and micropore region, had excellent potential as an adsorption material for achieving high removal and recovery of 4-nitrophenol from the contaminated water. These results will also advance the understanding of the adsorption and desorption behavior of hyper-cross-linked polymer resin in the wastewater treatment systems.