Preparation And Characterization Of Biochars And Their Influences On Adsorption And Desorption Of Sulfur Onto Light Sierozem

Biochar is a stable and highly aromatic carbon-rich substance which is prepared at high temperature through pyrolysis of biomass(such as straw,agricultural products processing,livestock manure and other agricultural and forestry residues waste)under oxygen-limited conditions.It has a very rich pore structure,large surface area,strong adsorption,rich charge and functional groups of surface and so on.It will affect the interface process and migration of nutrient elements when input soil.In addition,biochar contains abundant mineral elements,which can promote the growth and development of plants.Biochar as a new type of environmental function and soil improvement materials,not only provides a new way for the reuse of agricultural waste resources,and show great potential for crop cultivation and soil nutrient retention.It can foreknow that biochar will bring tremendous social and economic benefits of reducing greenhouse gas emissions,improving and controlling the pollution of soil.It also has more broad application prospects in ecology,soil science and agricultural production.In recent years,with the development of agriculture in China,more and more sulfur is taken away from the soil,but the amount of sulfate fertilizers put into the soil-plant system is decreased,which leads to the expansion of the soil lacking in sulfur.Crop stalk and animal feces resources of China are very rich,but the current utilization technology of crop stalk and animal feces resources is underdeveloped,resulting in a waste of biomass resources.Domestic and foreign scholars have made a systematic study to solve this problem.So far,the domestic and foreign research about adsorption of sulfate on biochar of potato straw and pig manure is rare.In order to define the influences of biochars which were derived from the local agricultural waste on the adsorption of sulfate onto light sierozem,biochars in this paper were prepared from potato straw and swine manure which are typical agricultural wastes in Gansu province at 300?,500? and 700? and respectively labeled as BPS300,BPS500,BPS700,BSM300,BSM500 and BSM700.After the optimization of adsorption,BPS700 and BSM700 were selected as the objective biochars.The structure and composition of the selected biochars and light sierozem were characterized by scanning electron microscope,surface pore size analysis and so on.To explore the adsorption characteristics of sulfate,the effects of contact time,pH value of solution,initial concentration,temperature on adsorption or desorption of sulfate onto biochar,light sierozem and light sierozem with biochar were tested using the batch equilibrium method.The results could provide theoretical basis to the application of biochar into soil,the application and regulation of sulfur fertilizer,and the quality of agricultural products.The main results are as following:The ash content and productivity of biochar were closely related to the temperature of carbonization,the ash content of BPS and BSM increased with the increase of the temperature of carbonization,while the productivity decreased gradually.The aromatization degree of BPS is higher,while the polarity and hydrophility of BSM is stronger.The adsorption amount of BPS and BSM on sulfate increased with the increase of the preparation temperature,so BPS700 and BSM700 were selected for the following experiments.The sequence of specific surface area of BPS700 and BSM700 is BPS700 > BSM700,the average pore size of the three substances have a big difference,the sequence is BSM700 > BPS700.There is no obvious pore structure of light sierozem,the small pore structure of BPS700 is more,the structure of BSM700 is a group of solid state.BPS700 and BSM700 have-OH,-COOH,R-COO-R',and light sierozem has a large number of mineral elements and organic matter.The adsorption of sulfate onto BPS700,BSM700,light sierozem and light sierozem with biochars was researched.The results showed that adsorption amount of sulfate increased with time,and finally reached the adsorption equilibrium.In the first two hours,the adsorption rate of sulfate was very fast,and it reached equilibrium after eight hours.The adsorption kinetics followed the pseudo second order equation.The adsorption amount of sulfate onto five adsorbents increased with increasing initial concentration of sulfate.The adsorption isotherm fitted the Langmuir-Freundlich and Temkin model.The adsorption kinetics of sulfate onto BPS700,BSM700,light sierozem and light sierozem with biochar were spontaneous.The adsorption amount of sulfate increased with increasing initial pH value of solution and temperature.In general,the sequence of adsorption amount of sulfate is LS > BPS700+LS > BSM700+LS > BPS700 > BSM700,while the coexisting anions have less effect on the adsorption of sulfate.The desorption of sulfate from BPS700,BSM700,light sierozem and light sierozem with biochars was researched.The results showed that desorption amount of sulfate increased with time,and finally reached the desorption equilibrium after six hours.The sequence of desorption amount of sulfate is LS > BPS700+LS > BSM700+LS > BPS700 > BSM700.The desorption kinetics followed the pseudo second order equation.The desorption amount of sulfate from five adsorbents increased with increasing initial concentration of sulfate.The desorption amount of sulfate increased when the initial pH values of solution were more than 4 in biochars system,and the desorption amount of sulfate increased when the initial pH values of solution were more than 6 in light sierozem and light sierozem with biochars system.The desorption amount of sulfate from light sierozem increased with increasing temperature,while it has less effect for biochars and light sierozem with biochars system.