Study On Sorption Characteristic Of Tea Waste Modified By Nano Hydrated Manganese Oxide Toward Ionic Pollutant

With the rapid development of China's industry agriculture and the economy,the pollutants discharged into the environmental media have constantly increased year by year,and the environmental quality has greatly declined.In recent years,the concentration of ionic pollutants(such as heavy metals,phosphorus,nitrogen,etc.)in various environmental media has been far more than the national control standards of the situation,which is seriously harmful to the ecological system and human health.Therefore,the development of cost-effective means to restrain the expansion of ionic pollutants has always been a hot topic in the field of environmental protection.Tea waste(TW)was modified by depositing hydrated manganese oxide(HMO)onto it through in situ precipitation and a novel hybrid bio-adsorbent,namely HMO-TW,was obtained and characterized by SEM,TEM,XRD and FTIR spectroscopy.The adsorption properties of four typical heavy metals(i.e.,Pb2+,Cd2+,Cu2+,Zn2+)by HMO-TW on heavy metal ions in water were investigated.The removal of by HMO-TW was pH-dependent,and higher pH favored the sorption at tested pHs of 2-7.HMO-TW showed excellent sorption selectivity toward all four metal ions,and the removal efficiency of target metal ions sustained at 30%?90%even in the presence of 50 times higher competing Ca2+ and Mg2+ ions.Sorption isotherms of four metal ions by HMO-TW are all well represented by the Freundlich model,and the maximum experimental sorption capacities of Pb2+,Cd2+,Cu2+,Zn2+ were 174.3,78.38,54.38 and 37.5 mg/g,respectively.Compared to the unmodified tea waste,the sorption capacities and selectivity of Pb2+,Cd2+ and Cu2+ onto HMO-TW improved significantly.The sorption process reached equilibrium within 200 min,and the kinetics could be well fitted by a pseudo-second order model.Fixed-bed column sorption results further showed that bed volume(BV)of Ce/C0 reaching 0.5 for Pb2+,Cd2+,Cu2+,Zn2+ were 1170,1130,820 and 1450 BV,respectively.All results reported herein validate that HMO-TW is a promising sorbent for practical treatment of heavy metal contaminated water.In addition,the feasibility of the composite adsorbent for the exhausted purification of phosphorus-containing wastewater was also evaluated based on the idea of treatment of wastes with processes of wastes against one another,which provided a new idea for the subsequent treatment of adsorbed saturated adsorbent.The enhancement of phosphate adsorption by the sorbed lead was first validated using several types of raw or modified waste biomass.Tea waste-supported hydrated manganese dioxide(HMO-TW)with the highest Pb sorption capability,HMO-TW(Pb)was then chosen to systematically evaluate phosphate retention.Phosphate adsorption onto lead-laden HMO-TW(HMO-TW(Pb))waspH-insensitive with only slight decline at pH>8.5,and was barely affected by competing anions owing to the specific surface precipitation mechanism.Additionally,the phosphate adsorption onto HMO-TW(Pb)was quick(with equilibrium time<60 min)and barely affected by temperature.Moreover,no signs of lead leakage from HMO-TW(Pb)were observed during phosphate adsorption at a wide pH range(4.2-11.3)and high ion strength(0-250 mg/L NaNO3).The lead on HMO-TW(Pb)was greatly stabilized through phosphate retention,which also reduced the environmental risks of their following treatment.Fixed-bed column test further suggested that HMO-TW(Pb)has practical applicability in efficient removal of phosphate from water.