Fabrication Of A Novel Hydrous Zr(?) Oxide-based Nanocomposite For Enhanced Heavy Metal Removal From Water

Water pollution by toxic metals is a global environmental concern now,and enhanced removal of heavy metals from water is still an urgent task for ecological safety and human being health.In general,the currently available technologies for decontamination of water from heavy metals are still far from satisfaction,and further study is still required then.One of the hot topics to respond to this challenging task is to develop new materials of preferable adsorption toward heavy metals,good reusability,and satisfactory mechanical and hydraulic properties.Hydrated zirconium oxide(HZO)is amphoteric in nature and has proved to exhibit high capacity of some inorganic pollutants.Here,particulate HZO was prepared through alkali precipitation and well characterized by BET,FT-IR,XRD,TGA,and size distribution in water.The HZO particles were very stable in an acidic solution(e.g.,pH=1).The uptake of Pb(II)and Cd(II)increased with the increase of solution pH to 6,and the isothermal adsorption could be well represented by the Langmuir equation.Unexpectedly,HZO adsorption was enhanced when the ionic strength of solution increased.It was possibly because the ion exchange between anions(i.e.,NO3-,Cl-,ClO4-)in solution and hydroxyl groups binding the surface of HZO promoted the hydrolysis of heavy metal ions in solution,and the hydrated metal ions are of low hydration engenry and high perferance for HZO adsorption.In addition,the enhancement effect of anions seems stronger than the competitive effect of the coexisting cations on metal uptake.However,HZO is usually present as fine particles and cannot be readily employed for flow-through systems due to the excessive pressure drop and poor mechanical rigidity.To overcome the above obstacles,nanosized hydrated Zr(?)oxide was irreversibly impregnated inside a commercial cation exchange resin D-001,and we obtained a new nanocomposite HZO-001.HZO was present as amorphous nanparticles of 10-20 nm in diameter.When solution pH was above 1.0,no leaching of Zr from HZO-001 was measured.Pb(?)and Cd(II)adsorption onto HZO-001 was essentially an ion exchange process.As compared to D-001,HZO-001 showed more preferable adsorption toward both toxic metals from the background Ca(?)solution at greater levels.Both Pb(?)and Cd(?)adsorption onto HZO-001 could be represented by the Freundlich isotherm model and pseudo-first order kinetic model well,with the maximum capacities of 319.4 and 213.7 mg/g respectively.The synthetic Pb(?)or Cd(?)solution containing other ubiquitous metal ions was employed as the feeding influent for column adsorption,and the results indicated that the treatable volume of HZO-001 is around 3-4 times that of D-001 before reaching the breakthrough point set according to the effluent discharge standard of China.Also,the concentration of Pb(?)and Cd(?)could be reduced to lower than the limits of drinking water standard of WHO.The exhausted HZO-001 could be effectively in-situ regenerated by HNO3-Ca(NO3)2 binary solution for repeated use without any significant capacity loss.In addition,HZO-001 presents more preferable sorption of Pb(?)than its mixture of D-001 and HZO in the background Ca(?)solution at greater levels.Donnan membrane effect of the host D-001 and nanosized effect of HZO were belived to responsible for such cooperative effect of HZO-001.Effect of the host charge nature on the adsorption of the corresponding HZO composites was also examined,and the results revealed that both charged hosts(one is negatively charged and the other is positively charged)are more favorable than the neutral one to improve the dispersion of nan-HZO.Consequently,the former two composites exhibit much higher capacity than the latter one for Pb(?)retention.On the other side,the negatively charged host could result in much higher capacity of the composite than the positively charged one because of their different Donnan effect.XPS study revealed that the specific interaction HZO and Pb(?)is stronger than the electrostatic attraction between SO3-and Pb(?).Consequently,with the increase of Ca(?)levels in solution,the immobilized HZO nanparticles contributed more than the host D-001 to the total Pb(?)uptake by HZO-001.Use HZO-001 in treatment of acidic mining effluent was examined in fixed bed adsorption to further validate its applicability in practical application.The effluent had a pH value of 3.36 and contained diverse competitive cations 3200 times higher than Pb(?)at molar concentration.HZO-001 could remove Pb(?)from 1.15 mg/L to<0.5 mg/L(Chinese standard for discharge of mining effluent),with the treatable volume 13 times higher than that of D-001.Meanwhile,other metal species like Cr and Cu were also thoroughly removed from the effluent.The exhausted HZO-001 could be effectively in-situ regenerated by HNO3-Ca(NO3)2 binary solution.In summary,a novel nano-Zr(?)-encapsulated hybrid adsorbent was prepared by impregnating HZO nanoparticles within porous caion-exchanger resin D-001.The resulting adsorbent exhibited high acidic resistance and selective adsorption on heavy metals.The exhausted hybrid adsorbent could be effectively regenerated by acidic solution for repeated use without any significant capacity loss.We believe that the current study is significant to develop advanced treatment techniques for enhance toxic metal removal from water,and serve as reference to fabricate highly efficient materials of similar structure for environmental remediation.