Study On The Removal Of Heavy Metal Ionsfrom Water By Sludge Biochar Loaded Withnanometer Zero-valent Iron

In recent years,due to the rapid development of urbanization and industrial production,a large amount of heavy metals have entered the water environment as a result.The disadvantages that heavy metals are hard to degrade,highly toxic and easily accumulate in living organisms make them a serious threat to human beings as well as plants and animals and the natural environment.Therefore,it is urgent to develop efficient and green heavy metal adsorption materials.Nanometer zero-valent iron（NZVI）is widely used to remove heavy metals due to its large specific surface area and good removal effect.However,nano zero-valent iron alone suffers from the disadvantages of easy oxidation and agglomeration,which limits its use in the real reality.In this paper,we used biochar prepared from municipal sludge as a carrier to load NZVI,reduce its agglomeration and oxidation,and produced nano zero-valent iron composites（Na OH@SB-NZVI）and sludge biochar（SB）loaded NZVI（SB-NZVI）for Cu²⁺and Cd²⁺removal with alkali-modified sludge biochar as a carrier,respectively,to investigate their removal performance and mechanism.The main elements and conclusions are as follows:NZVI and Na OH@SB-NZVI were produced by liquid-phase reduction and SB was produced by high-temperature pyrolysis.the optimal preparation conditions（sodium hydroxide concentration,pyrolysis temperature,solid-liquid ratio,and modification time）of alkali-modified sludge biochar（Na OH@SB）were optimized by orthogonal experiments.The results showed that Na OH concentration of 3 mol/L,pyrolysis temperature of 500°C,solid-liquid ratio of 1:20 and modification time of 24 h were the best modification conditions for SB,and the maximum adsorption capacity of Na OH@SB for Cu²⁺was 183.22 mg/g,which was 2.43 times of the original sludge biochar.The batch experiments showed that the removal capacity decreased with the increase of adsorbent dosage,increased with the increase of Cu2+concentration and p H,and the presence of coexisting ions Na⁺,Ca²⁺and Mg²⁺as well as humic acid（HA）inhibited the removal of Cu²⁺to some extent.The adsorption behaviors of the four materials,SB,NZVI,Na OH@SB and Na OH@SB-NZVI,were in accordance with the the pseudo-second-order kinetic model,indicating that the removal of Cu²⁺was mainly caused by chemisorption.The adsorption isotherms were in accordance with the Langmuir model,and the maximum adsorption capacity of Na OH@SB-NZVI for Cu²⁺was 358.42 mg/g at p H=5 and 25°C,which was 2.40 and 1.96 times higher than that of SB,NZVI和Na OH@SB的4.76,respectively,indicating the superior adsorption performance of the composites.Reproducibility tests confirmed the good reproducibility and stability of the materials.characterization results such as FTIR,XPS and XRD indicated that the mechanism of Cu removal by Na OH@SB-NZVI composites involved several processes such as adsorption,precipitation,electrostatic attraction and reduction.In addition,SB-NZVI composites were synthesized for Cd²⁺and Cu²⁺removal using a carbothermal reduction method.The best removal capacity was 55.94 mg/g for Cd²⁺and 97.68 mg/g for Cu²⁺at a mass ratio of iron to sludge of 1:4 and a pyrolysis temperature of 900°C.Batch experiments showed that the SB-NZVI（1:4-900）composite had good removal capacity for Cd²⁺and Cu²⁺over a wide p H range,with weakly acidic to The XPS results showed that the removal of Cd²⁺was mainly dependent on adsorption and precipitation/co-precipitation,while reduction and adsorption were the decisive mechanisms for Cu²⁺removal.Also the removal experiments showed that the effect of Cu²⁺presence on the removal of Cd²⁺showed that low concentration promoted high concentration inhibition,while the presence of Cd²⁺had less effect on the removal of Cu²⁺.Through this paper,it can be concluded that biochar prepared from municipal sludge is effective as a carrier for NZVI,Na OH@SB-NZVI prepared using liquid phase reduction method can effectively remove Cu²⁺from water,and SB-NZVI prepared by carbon thermal method can be used for simultaneous removal of Cd²⁺and Cu²⁺with good removal effect.This study provides a new option for the resource utilization of municipal sludge and the treatment of heavy metal wastewater.