Research On The Preparation Of Sludge-based Biochar And Its Adsorption Performance For Hg²⁺

With the rapid development of economy of our country and the rising of the living standards of the people, the people’s demand of material boosts up, this leading to the increasing of the quantity of sewage sludge in recent years. The large amount of sewage sludge has become a significant burden.It is a new research hotspot to treat sludge in innocuous method.This thesis aims at reusing sewage sludge as a resource in the way of preparing biochar from sewage sludge, and the municipal sludge of Urumqi is taken as raw material. With low-temperature pyrolysis method, the influences of different additives and process conditions on the pyrolysis reaction were researched in order to produce sludge biochar with large surface area and rich nutrient. BET, SEM and FT-IR were adopted to characterize the biochar, in addition, the adsorption isotherm and adsorption kinetics of Hg2 + of sludge biochar were studied.Firstly, KOH, KAC, KH₂PO₄, H₃PO₄ and KHCO₃ were added into the sewage sludge respectively as pyrolysis additives to pyrolysis the sewage sludge. Iodine and methylene blue test adsorption methods were used to characterize the adsorption capacity of the prepared biochar. The experimental results showed that the adsorption capacity of biochar is the best when the dosage of KAC（potassium acetate） was 4.0wt %. In this condition, the adsorption amount of methylene blue and iodine are 89.09 mg·g^-1, 236.63 mg·g^-1 respectively, and the p H value is 8.73. BET area has improved to some extent(13.433 m2·g^-1) compared to the sludge. The content of available nitrogen, available phosphorus, available potassium and organic matter of biochar are 394.10 mg·kg^-1, 260.18 mg·kg^-1, 222.50 g·kg^-1 and 224.49 g·kg^-1 respectively, so the KAC is selected as the additive agent finally.Secondly, on the base of KAC as the pyrolysis additive, the influence of pyrolytic reaction conditions（the additive amount of KAC, ultimate pyrolysis temperature, retention time and heating rate） on the adsorption performance of sludge biochar were investigated by orthogo nal test and single- factor experiments, and the best reaction conditions were determined. The optimum reaction conditions are as follows: the dosage of K AC is 4.0wt %, reaction temperature is 350℃, the retention time is 120 min and the heating rate is 3℃·min – 1. Under the optimum conditions, the adsorption amount of methylene blue and iodine are 90.45 mg·g^-1 and 382.17 mg·g^-1 respectively, the BET area was significantly increased to 31.402 m2·g^-1. At the moment, the total nutrient of sludge biochar was improved up to 5.58 %, which was far higher than the value of criterion of soil nutrient.Finally, the adsorption performance for Hg²⁺ of biochar prepared under optimum conditions was studied. The experimental results show that: when the p H value of the solution was 6, the initial mass concentration of Hg²⁺ was 15.0 mg·L^-1 and the dosage of adsorbent was 6.0 g·L^-1, the removal rate of Hg²⁺ on the biochar was over 97 % and the maximum adsorption capa city of Hg²⁺ was 2.87 mg·g^-1. After fitting these experimental data, it can been seen that the adsorption isotherm of Hg²⁺ was well fitted with Langmuir model at room temperature and the adsorption kinetics of Hg²⁺ was in conformity with the pseudo-second-order kinetics equations.