Preparation Of Thiol Modified Biochar And Its Remediation Of Heavy Metal Contaminated Soil

Soil heavy metal pollution can seriously threaten human and ecosystem health,therefore research and development of effective soil remediation technology is one of the hot spots in the frontier of science and technology.Chemical immobilisation technology has become an important remediation method for heavy metal contaminated soil due to its advantages of in-situ remediation,economical and easy operation,and the research on its core immobilisation materials has attracted much attention.Biochar is an important immobilisation material and the research hotspot is focusing on enhancing the immobilisation properties of biochar by modification.Thiol groups can form stable compounds with heavy metals.A large number of studies have shown that various types of thiol modified materials can immobilise heavy metals in environmental media,thereby reducing the risk of pollution.However,there are few studies on thiol modified biochar,so further research is urgently needed.In this study,through the comparison and analysis of different thiol loading methods and various combinations of biochar materials,the thiol modified biochar were successfully developed.The physical and chemical properties of thiol modified biochar were determined by a series of advanced analytical methods.The adsorption properties and mechanism of thiol modified biochar on typical heavy metals were discussed in combination with batch adsorption experiments,and the effect of thiol modified biochar on the speciation of typical heavy metals was studied by soil culture experiments.The main research results were shown below:（1）The mercaptoethanol（sulfuric acid）catalyzed esterification method can be successfully used to prepare the thiol modified rice s traw biochar.After thiol modification,the thiol functional group can be measured and the loading thiol group can reach 0.83?0.04 mmol·g^-1.The pH value and point of zero charge of the thiol modified biochar decreased obviously.The specific surface area and internal pore volume also decreased distinctly.The thiol modified biochar exhibited smooth morphology features.（2）The adsorption rate of typical heavy metal cadmium by thiol modified biochar was significantly improved,and the adsorption capacity was significantly enhanced.The adsorption capacity of cadmium by thiol modified biochar was increased by about 3 times,up to 45.13 mg·g^-1,and it was not easy to be desorbed,while cadmium adsorbed by rice straw biochar can be desorbed by 57%.However,the adsorption rate of typical heavy metal lead by thiol modified biochar decreased slightly,and the adsorption amount decreased by about 9%.X-ray photoelectron spectroscopy（XPS）analysis showed that thiol modified biochar adsorbed Cd²⁺and Pb²⁺may form more stable cadmium sulfide compound and lead sulfide compound.（3）After adding thiol modified biochar to the soil,pH value decreased significantly and organic matter content increased significantly,but soil cation exchange capacity did not change significantly.After addition of thiol modified biochar,the available content of Cd in soil was significantly reduced,with the largest drop of 39.18%in the 28-day soil culture experiments.The speciation of Cd changed greatly,in which the ratio of Fe/Mn oxide-bound Cd increased obviously,and the ratio of carbonate-bound Cd decreased obviously.The available content of Pb in the soil fluctuates a little,but the change is small.