Sorption Of Pb(Ⅱ) And Ionic Dyes From Aqueous Solution By Using Biochars

With the continuous improvement of the level of agricultural production and farmers’ life level, the use of agriculture and forestal waste for composting or feeding is damping and more and more agricultural and forestal waste was left. Unreasonable disposal of the waste will cause environmental pollution, e.g., serious air pollution was caused by the burning of straw in many rural areas in recent years. So the reasonable resource utilization of the agricultural waste can not only control agricultural environmental pollution, but also help to alleviate the pressure of the shortage of resources in our country, and will promote the sustainable development of agriculture. Among the utilization technologies of the agricultural and forestal waste, the pyrolysis of biomass in free or limited oxygen for preparing biochars receives more and more attentions. Biochar can not only help in carbon emissions reduction, but also can increase the content of soil carbon to modify or remediate the contaminated soil. Researches show that the biochars with the very extensive raw materials and simple preparation have high stability and part of the biochars have good adsorption performance. Therefore, biochars can be used in treatment of wastewater cheap adsorbents for the removal of pollutants. In this study, biochars were derived from different types of biomass feedstocks through pyrolysis at 600 oC in N2 or through hydrothermal method. Physicochemical properties of the resulting biochars were characterized using various methods. Sorption of Pb²⁺, methylene blue and congo red onto selecting biochars was carried out. The adsorption properties and mechanism were discussed to screen out low cost and high adsorption efficiency of adsorbents. Results were as follows: 1) The surface morphology, phase structure, specific surface area, thermal stability and the elemental composition of eight biochars derived from sweet beet tailing, sugarcane bagasse, peanut hulls, hickory wood, pine needles, moss, manure and biosolids were analyzed. The results showed that the physicochemical properties of biochars derived from feedstocks differed greatly. In aqueous solution, biochar would release mineral nutrients. Under acidic conditions, biochar would release some toxic heavy metals. The tested biochars are alkaline and the pHpzc is high.2) Effects of solution pH, initial concentration and reaction time on the adsorption of Pb²⁺, methylene blue and congo red onto biochars derived from hickory wood, pine needles, moss, manure and sludge were investigated. The results showed that pH exerted a great influence on adsorption of Pb²⁺, methylene blue and congo red. The adsorption capacity of the sewage sludge-biochar was greater than that of the plant-based biochars. The data of Pb²⁺ adsorption were better described by Langmuir equation than by Freundlich equation among the tested initial Pb²⁺ concentration range. The data of methylene blue and congo red were better described by Freundlich equation than by Langmuir equation among the tested initial Pb²⁺ concentration range of the dyes. Higher initial conentration of the aasorbates showed higher adsorption rate, but reached adsorption equilibrium later. Biochar’s adsorption data of three pollutants fitted the pseudo-second-order kinetic model, and the adsorption rate in the particle diffusion stage has an important influence on the adsorption rate of the whole process.3) Two hydrothermal biochars derived from grapefruit peel and rice husk were used to adsorb lead, methylene blue and congo red dye. The results show that the pH also affected the adsoption capacities obviously, similar to the case of the pyrolyzed biochars. Also the adsorption of Pb²⁺ fitted Langmuir equation better and the adsorption of the dye fitted the Freundlich equation better among the tested initial absorbates concentration range. The adsorption capacities of the grapefruit peel-biochar for three pollutants were greater than them of the rice husk-biochar. Reaction time experiments showed that the adsorption data for Pb²⁺, methylene blue and congo red biochars were well fitted with the pseudo-second-order kinetic model. Adsorption of Pb²⁺ and dyes were occurred mainly the first 2h.