| With the rapid development of China's economy,various heavy metal pollutants in the industrial production process enter the soil through various channels,which in turn makes the problem of heavy metal pollution in soil in China increasingly intensified.At present,the remediation technologies of heavy metal pollution in soil mainly include physical method,bioremediation and chemical curing method,etc.As a new and low-cost green material,hydrochar has the advantages of low price and environmental protection in the remediation of heavy metal pollution in soil by virtue of its high specific surface area.However,at present,the main research focuses on the stabilization and fixation of heavy metals in soil by different biomass hydrochar,while there are few researches on the remediation of heavy metal contaminated soil by modified hydrochar.In this paper,pine sawdust is used as a precursor,biochar is prepared by hydrocharization,and ammonium dihydrogen phosphate,phosphoric acid,and hydrogen peroxide are used to prepare hydrothermal charcoal.Scanning electron microscopy,specific surface area and pore structure analysis,infrared spectroscopy Characterized by technical means.In the adsorption experiment,the adsorption effect of the prepared hydrochar on Cr(?)in solution was discussed,and the adsorption mechanism was analyzed.On this basis,through the soil cultivation experiment,the stability of the prepared hydrochar to chromium in soil was discussed.The main conclusions are as follows:(1)The optimal preparation temperature of wood chip hydrochar(BC)is 240?,and the optimal preparation time is 4h.The surface p H of the four hydrochar are all acidic,and the zero charge point is about 4.0,which is helpful for the adsorption of acidic conditions the anion group under the water.The process of hydrocharization enriched the groups(-COOH?-CHO?-OH etc.)on the surface of carbon,and the number of acid functional groups such as hydroxyl group and carboxyl group increased.The N content in the ammonium dihydrogen phosphate modified hydrochar(NBC)has increased in combination with the infrared spectrum,it can be concluded that nitrogen-containing functional groups such as pyridine and amino groups have newly appeared on the surface of NBC,but the specific surface area of NBC has decreased by 40.04%.The O content of hydrogen peroxide modified hydrochar(OBC)is increased,the number of the groups(eg:-COOH?-CHO?-OH etc.)on the surface of OBC is increased,and the specific surface area is the largest,and the pores are the most developed.Phosphoric acid-modified hydrochar(PBC)carbon has rich oxygen-containing functional groups on the surface,which improves the aromatization of the carbon,but the corrosion of the activator reduces its specific surface area by 83.77%.In short,the modification methods used in this experiment have improved some characteristics of the wood chip hydrothermal charcoal from all aspects,thereby enhancing the adsorption stability.(2)For the adsorption of Cr(?)in solution,the adsorption capacity of hydrothermal charcoal decreases with the increase of p H.The efficiency of BC,NBC and OBC at p H=3 is the largest,and all of them reach more than 85%.When p H=2,the PBC has the maximum adsorption capacity.The increase in the amount of added carbon did not lead to an increase in the removal rate of Cr(?).The optimal amount of the four kinds of hydrochar was 8g/L.The increase in initial concentration improves the mass transfer power of ions,thereby increasing the unit adsorption capacity of hydrochar.The adsorption equilibrium time of BC,NBC and OBC was 24h,while PBC reached the adsorption equilibrium at 12h.The model fitting results show that the adsorption kinetics of the four hydrochar is more in line with the second-order kinetics model,R~2>0.99,and the diffusion fitting straight line within the particles does not pass through the origin,indicating the intraparticle diffusion was not the main factor limiting the adsorption process.The adsorption process belongs to the chemical adsorption where electron transfer occurs,and the adsorption rate is affected by many factors such as the solution ion concentration.The Langmuir model fitting of BC and PBC has more advantages.The adsorption process of these two hydrochar is mostly monolayer adsorption,while NBC and OBC are more in line with the Freundlich model,with homogeneous adsorption as the main.Modifications of ammonium dihydrogen phosphate and hydrogen peroxide have improved the adsorption capacity of hydrochar for Cr(?).NBC has the largest improvement,and its unit adsorption capacity has increased by 16%.(3)The results of soil cultivation experiments show that all four kinds of hydrochar can reduce the harmfulness of chromium in the soil to a certain extent.Among them,NBC has the greatest advantage in reducing the toxicity of chromium in the soil,from23.63%of the blank soil to 17.21%.The reduction of the toxicity of BC to chromium in the soil is less affected by the increase in the amount of carbon added.The remaining three hydrochar are positively related to the amount of chromium in reducing the toxicity of chromium in the soil,and 10%NBC is also the best.With the extension of cultivation time,NBC has a persistent advantage in stabilizing chromium-contaminated soil due to its rich functional groups and large specific surface area. |
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