Preparation Of Tetraethylenepentamine Modified Bentonite And Its Adsorption To Copper, Nickel, Cadmium

With the development of industry and agriculture, human beings wantonlydestructed the ecological environment in order to pursue economic interests. The soilheavy metal pollution is becoming one of the most important environmentalproblems. On April17,2014,<<The communique of national soil pollutioninvestigation>> was issued by the Ministry of Environmental Protection and theMinistry of Land and Resources. It pointed out that the total over standard rate ofnational soil was16.1%, the pollution of inorganic heavy metals such as cadmiumwas the main pollution. Therefore, the control of heavy metals pollution soil should becarried out immediately. Bentonite is a kind of natural clay with advantage of largereserves, stable physical and chemical properities, and good adsorptive ability toheavy metals. The application of original bentonite and modified bentonite to heavymetal contaminated soil had caused the attention of many researchers. In this study,the present situation of heavy metal pollution, the properties, the modification and theapplication of bentonite had been reviewed, and the amine-modified bentonite hadbeen prepared with TEPA. The adsorption mechanism of amine-modified bentonite tocopper, nickel and cadmium had been discussed, and then it had been applied to repaircopper, nickel and cadmium contaminated soil. The results came from the studyprovided a valuable application material for soil heavy metal pollution and hadtheoretical and practical significance. The main research works and achievementswere as follows:1. The simple solution method was adopted to prepare amine-modified bentonitewith TEPA as the modifier, the influence of the amount of TEPA, liquid-solid ratio ofreaction, reaction time and temperature were investigated. And the structure ofamine-modified bentonite was characterized by the methods of FT-IR, XRD andthermal analysis, and the specific surface area and ion exchange capacity weremeasured. The optimum preparation conditions were: the reaction liquid-solid ratio (mL/g) was40:1, the dosage ratio of bentonite to TEPA (g/mL) was1:0.05, thereaction temperature was room temperature and reaction time was5h.2. The amine-modified bentonite was used to adsorb Cu2+, Ni2+and Cd2+fromaqueous solution, the effect of adsorbent dosage, solution pH, ionic strength,adsorbent time and adsorbent temperature on the adsorption were studied, and theadsorption ability of modified bentonite and original bentonite was compared. Whenthe adsorbent dosage was5g/L, solution pH was5.0~6.0(copper solution was5.0,nickel and cadmium solution is6.0), ionic strength was0.1mol/L KNO3medium,adsorbent temperature was room temperature, the saturated adsorption capacity ofamine-modified bentonite to copper, nickel and cadmium were395.74,395.74,352.18mmol/kg, they were12.84,10.24,15.41times that of the original bentonite,the adsorption capacity was siginificantly higher than original bentonite. After themodification, the adsorption selectivity of metals was different, the sequence oforiginal bentonite was Ni2+>Cu2+>Cd2+, but the amine-modified bentonite adsorptionorder was Cu2+>Ni2+>Cd2+.3. The desorption properties of simulated acid rain for Cu2+, Ni2+and Cd2+hadbeen discussed. When the pH of simulated acid rain was3.5, ionic strength was0.3mmol/L, oscillation desorption time was60min, the desorption temperature was roomtemperature, the desorption rates of copper, nickel and cadmium were belove0.2%,1.0%and1.0%, respectively. Amine-modified bentonite had a strong adsorptionability for copper, nickel and cadmium, natural acid rain could hardly desorb heavymetals which adsorbed by amine-modified bentonite.4. The adsorption mechanism of amine-modified bentonite had been investigatedby adsorption thermodynamics study, adsorption desorption kinetics study andstructural characterization. The adsorption thermodynamic behavior of Cu2+、Ni2+and Cd2+on amine-modified bentonite followed Freundlich isotherm models, the R2was more than0.99, the values of△G were negative and△H was positive, thekinetic behavior could be described well with quasi-second order kinetic equation,which the R2was more than0.999. It turned out that the adsorption process was amultilayer, heterogeneous, chemical reaction process, and it was a spontaneousendothermic reaction. Desorption process was justly on the contrary, the heavy metalwhich tend to be adsorbed was not easy to be desorbed. The adsorption ofamine-modified bentonite to Cu2+、Ni2+and Cd2+were given priority to aminocomplexation, followed by ion exchange.5. The soils from Chengdu University of technology were collected and culturedby copper, nickel and cadmium, then original bentonite and amine-modified bentonitewere added into the contaminated soils. The effect of soil restoration was evaluated bythe chemical extraction experiment. The extraction ratio of copper, nickel andcadmium by simulated acid rain was very low, were all below0.1%, amine-modifiedbentonite had strong passivation ability to heavy metal in soil under the natural condition. The extraction rate substantially increased when the mixed extracting agentwas used, and the metal ions extraction rate of amine-modified bentonite repairedsoils were significantly lower than the other two types of contaminated soil, it showedthat the adsorption ability of amine-modified bentonite to Cu2+、Ni2+and Cd2+wasstronger than original bentonite, and it had repairing ability to repair heavy metalcontaminated soil.