Preparation And Characterization Of Biochar From Water Hyacinth And Its Adsorption Properties Research On Cadmium

This study mainly focused on biochars from water hyacinth(Eichhornia crassipes) at different pyrolysis temperature by using methods for chemical analysis and technology of spectroscopic characterization to analyze structure, physical and chemical properties of biochars. Performance and mechanism of adsorption of heavy metal cadmium were studied. Adsorption process of cadmium by biochars and effects on cadmium removal of ash content was clarified in this study. An important theoretical foundation was provided in the terms of application of biochars in heavy metal removal, which provided a new way to solve two severe problems(excessive reproductions of water hyacinth and heavy metal pollution).The main original conclusions of this work are drawn as follows.(1) Cd adsorption performance of water hyacinth biochars: biochars at different temperature have highest removal rate of 99.24% and high adsorptive capacity with the average removal rate of 94.71%. Considering energy saving, biochars at 300℃ have highest cost effectiveness. When compared with other biochars from Rice, corn stalks at 500℃(the average removal rate of over 95%), to maintain high removal rate, the preparation temperature of water hyacinth biochars is lower, which is beneficial to energy saving.(2) Yield: WH300(the prefixes “WH” are the abbreviated form of water hyacinth, and the number following “WH” represents the pyrolysis temperature)The highest yield of WH700 is 46.59% and lowest yield is 28.20%. With the preparation temperature increases, the yield declines.(3) pH value:With the increase of preparation temperature, the pH value increases. The pH value of WH300 is lowest(7.98), and the pH value of WH700 is highest(11.54).(4)ash content, specific surface area etc:WH300 has the lowest ash content of 15.89%,WH700 has the highest ash content of 37.25%. With the increase of preparation temperature, ash content and aromaticity increase while chemical polarity and hydrophilicity decrease. Besides, specific surface and Vtotal of biochars increase to be developed micro-pore structure.(5) Cd adsorption mechanism:Kinetics model of Cd adsorption is pseudo-second order kinetic model; WH300, cadmium can react with its deprotonized functional groups(-COO and-O) by complexation, with the slow release of OH. Higher temperature biochar(WH500 and WH700) showed the precipitation occurred between cadmium and the inorganic minerals. With the increase of pH value, removal rate of cadmium increases; absorption isotherm is Langmuir model(6) Water hyacinth biochars does not need deashing:the average removal rate of WH300、WH500 and WH700 is 94.15%、93.51% and 96.46% respectively. After deashing,the average removal rate of DWH300、DWH500 and DWH700 is 96.41%、53.10%�'� 21.35% respectively, which fall by 43.22% and 77.86% compared with the average removal rate before deashing.Biochars from water hyacinth have high removal efficiency, indicating good effect of heavy metal removal and adsorption performance of biochars from water hyacinth at low temperature. After removing ash, effect of cadmium removal declined. In practical application, process of ash removal could be leaved out for saving costs.