Preliminary Study On Modification Of Biochar And Its Effect On Heavy Metal Zn Passivation

With the rapid development of industrialization,heavy metal-containing waste water produced in a series of industrial processes such as mineral exploration,metal smelting and tailings piling will enter the water body and soil environment through different ways,which brings serious harm to human health.Therefore,it is urgent to develop new materials with obvious effect and low cost for heavy metal contaminated wastewater containing heavy metal and farmland.Biochar adsorbent is widely used in heavy metal pollution treatment because of its advantages of low price and easy adsorption,significant adsorption effect,and the availability of resources.However,in general,biochar processed from biological substrates has much less heavy metal adsorption than traditional activated carbon.The present study found that by chemical modification can improve the biochar adsorption capacity of heavy metals.In this study,the removal rate of Zn was taken as the optimization index.Biochar?BC?and corn stalks prepared from corn stalks were used as raw materials.The response surface methodology based on single factor experiment was used to optimize biochar?K-BC?and acid-washed biochar?H-BC?.And this is the adsorbent to explore its adsorption of zinc in simulated wastewater and its passivation effect on zinc in contaminated soil.The main research results are as follows:1.According to the response surface test,the K-BC modification optimum conditions:KOH concentration of 15%,the solid-liquid ratio of 1:15,carbonization temperature of 450?,carbonization time of 2h,when KOH adsorption of Zn The optimum conditions for H-BC modification were as follows:the concentration of mixed acid was 1 mol·L^-1,the carbonization temperature was 450?and the carbonization time was 2 h,the adsorption rate of Zn to H-BC could reach 31.23%.2.The results indicated that adsorption process of Zn on BC,K-BC and H-BC were consisted of the rapid and slow section at Zn concentration of 60 mg·g^-1,and Quasi-second-order kinetic adsorption model could be better to described their adsorption process.And combined with the intraparticle equation,it can be seen that the rate of Zn adsorption by these three biocokes is controlled jointly by liquid film diffusion and intragranular diffusion3.The adsorption capacity of Zn on BC,K-BC and H-BC increased with the increasing of temperature from 288 to 318K and Zn concentration from 10 to 120 mg·g^-1,and the adsorption process was well fitted to the Freundlich equation.Thermodynamic parameters revealed that Zn adsorption by BC,K-BC and H-BC were a feasible,spontaneous and endothermic process with an increase in disorder.4.Over the pH rang of 2.0⁵.0,the biochar of BC,K-BC and H-BC showed the highest5.Adsorption of Zn at pH 5.0,Over the Na⁺range of 0.01¹.0 mol·L^-1,the adsorption amount of Zn by these three biochar decreases with the increase of Na⁺concentration;In the concentration range of 5⁴0 mg·L^-1,when the concentration of citric acid is below 20 mg·L^-1,the Zn adsorption on the three biochar is promoted,while the concentration of citric acid is higher than 20 mg·L^-1 play a suppressive role.6.According to the structural characterization and physical and chemical properties of BC,K-BC and H-BC,it is obvious that differences in adsorption of Zn by BC,K-BC and H-BC derived from their specific surface area,pore structure and fragrance structure.7.The effects of BC and K-BC biochar on soil pH,organic carbon and available zinc content were studied by static culture at constant temperature?25??in laboratory.The results showed that compared with the control,adding different proportions of BC and K-BC can significantly reduce the available zinc content in the polluted soil,and can significantly increase the pH value of the acidic soil and the organic carbon content in the soil.The correlation analysis showed that the available zinc content was negatively correlated with soil pH and organic carbon content.