The Research Of Its Adsorption Properties For Cd²⁺ In Solution By Modified White Shell

In the aims of utilizing the agricultural or forestry wastes, a cost-effective absorbent to heavy metal was invesigated. In this work, natural white shells,the white shells modified with the 1% KMnO4 solution to make material named WSK, and white shells made into biochar then modified with the 1% KMnO4 solution to make material named MWSB-K, were prepared for absorbing Cd2+ in solution.The effects of particle size, temperature, dosage, pH, original Cd2+ concentration and time were investigated on the WS adsorption to Cd2+. The adsorption mechanisms were discussed and analysed in this paper based on the adsorption model, SEM and FTIR results. The effects of temperature, pH, time and original Cd2+ concentration were aslo investigated on the WSK adsorption to Cd2+. The adsorption mechanisms were also discussed and analysed in this paper based on the adsorption model, SEM and FTIR results. The effects of particle size and temperature were aslo investigated on the MWSB-K adsorption to Cd2+ The orthogonal optimization of adsorption experiment were designed with three factors temperature, initial concentration and pH of the solution for Cd2+. The adsorption mechanisms were discussed and analysed in this paper based on the SEM and FTIR results.Result indicated that:(1) The main chemical group of white shell were acid insoluble lignin and cellulose, pentosan and 1% NaOH extract also contained more.WS has the adsorption capacty of Cd2+. The adsorption ability of WS affected by article size, temperature, dosage, pH, original Cd2+ concentration and time.Conctectly, the optimal conditions were size of 0-2mm, the optimum pH=5,and after about 30mins, the adsorption process achieved balance.As dosage of 0.5g, volume of solution of 50ml, original Cd2+ concentration of 20mg/l, the adsorption capacity of Cd2+ was the biggest. While the original Cd2+ concentration of 100mg/l, dosage of 0.5g and volume of solution of 50ml,the removal rate of Cd2+ achieved 99.99%.Above all the factors, temperature had the least effect on adsorption. The adsorption of Cd2+fitted the second-order kinetic adsorption model with R2 of 1, which proved that the adsorption reaction mainly belonged to the chemical adsorption. Adsorption of Cd2+ data could aslo fit the Langmuir and Freundlich model with R2 of 0.98 and 0.94.It proved that the adsorption relyed mainly on surface adsorption and multilayer adsorption, and the largest adsorptivity could arrive at 17.23mg/g. IR-spectrum results inidcated that the adsorption of Cd2+ on WS was the co-action of the ion-reactive functional groups such as -OH,-COO,-NH-, C=O,-P=O and-CH-.(2)WSK could be regared as an ideal absorbent for Cd2+. The adsorption capacity affected by temperature, pH, reaction time and original concentration of Cd2+. Concrectly, the adsorption capacity enhanced as the temperature was increased. With the increase of pH, the adsorption capacity was initially enhanced and weakened, with the peak at 5.5. The adsorption would be in balance in 60 mins. The adsorption of Cd2+ was enhanced with the original Cd2+ concentration increased. The peak adsorption could be achieved when the concentration was 300mg/L, with the removal rate of 94.49% achieving the saturation adsorption. Adsorption of Cd2+ data could fit the Freundlich model with R2 of 0.94, and the largest adsorptivity could arrive at 119.76mg/g. The adsorption also fitted the second-order kinetic adsorption model with R2 of 0.9995. SEM images indicated the polyporous surface on the WSK, which achieved the adsorption ability by developing specific surface area, aperture volume, and increasing the surficial absorbing spots. IR-spectrum results inidcated that the adsorption of Cd2+ on WSK was the co-action of the ion-reactive functional groups such as-OH,-COO,-NH-, C=O,-P=O and-CH-, and the-COO- played an important role.(3) White shells were made into biochar and then modified with the 1% KMnO4 solution to make material named MWSB-K,whose adsorption capacity were about 5-6 times as modified before. The optimum particle size was 0.15-0.2mm. With the increase of temperature, the adsorption ability of Cd2+ was enhanced by using MWSB-K for the removal rate of 99.54% and adsorption capacity of 49.27mg/g. From the orthogonal optimization of adsorption experiment with three factors temperature, initial concentration and pH of the solution for Cd2+, it showed that the original concentration of Cd2+ had the biggest effect on the removal efficiency, then the pH, and at last the temperature.The optimization of experimental structure was pH of 5.4, tempeature of 45.6℃ and initial concentration of 369.8mg/l. Under the above conditions, predictive model of the removal rate of Cd2+ could achieve 99.88% and adsorption capacity be 152.34mg/g. SEM images indicated that the MWSB-K was the polyporous, rough, multi-channel of surface and polyporous of internal surface material, which achieved the adsorption ability by developing specific surface area, aperture volume, and increasing the surficial absorbing spots. IR-spectrum results inidcated that the adsorption of Cd2+ on WSK was the co-action of the ion-reactive functional groups such as-OH、C-O-C、-CO、C=O and C=C, and theC=C played an important role.