Clean Coal Technology

2022, v.28;No.142(06) 184-191

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Experimental study on ultrasonic-assisted leaching of biomass fly ash

HAN Kuihua;LIU Wenyang;SONG Chuanlin;REN Ke;TENG Zhaocai;NIU Shengli;WANG Yongzheng;ZHU Yingquan;LONG Shenwei;School of Energy and Power Engineering,Shandong University;Shandong Engineering Laboratory for High-efficiency Energy Conservation and Energy Storage Technology & Equipment,Shandong University;Shandong Fengyuan Biomass Power Generation Co.,Ltd.;

Abstract:

The fly ash produced from biomass power generation boilers is generally used as building materials and auxiliary materials for fertilizer production. However, the hazardous components in fly ash can reduce the stability of building materials and cause the enrichment of heavy metals in farmland. Therefore, the pretreatment of fly ash raw materials and the improvement of suitability are the key issues. In this study, fly ash from biomass power plant was used as raw material to obtain fine ash with particle size <0.2 mm by sieving. Fine ash and deionized water were prepared into slurry, which was treated by ultrasonic-assisted leaching and filtration. The effects of sonication time, slurry temperature, solid-liquid mass ratio on the leaching of macroscopic metal elements K,Na, Zn, Ca, and four trace heavy metal elements Co, Cr, Ni, Pb were investigated. The appropriate operating parameters were explored. The results show that the fine ash used in the experiment is rich in CaO,SiO_2 and K_2O. For macroscopic metal elements, the leaching concentration and leaching amount of metal elements increase and tend to be constant with the time prolonging within 1-30 minutes of sonication. While Ca(2+) increases first and then decreases slowly due to carbonation reaction. In the range of slurry temperature from 25 ℃ to 70 ℃,Ca(2+) increases first and then decreases slowly due to carbonation reaction. In the range of slurry temperature from 25 ℃ to 70 ℃,Ca(2+) generation and carbonation are significantly affected by temperature. With the increase of slurry temperature, the leaching mass concentration of Ca(2+) generation and carbonation are significantly affected by temperature. With the increase of slurry temperature, the leaching mass concentration of Ca(2+) increases firstly and then decreases, but the leaching mass concentration and leaching amount of other metal elements increase. In the range of solid/liquid mass ratio 1∶3 to 1∶6,the leaching concentration of metal elements decreases and the leaching rate of metal elements increases with the decrease of solid/liquid mass ratio. When sonication time is 20 min, the slurry temperature is 50 ℃,and the mass ratio of solid to liquid is 1∶5,the leaching rate of potassium reaches 47.22%. Sonication time, slurry temperature and solid-liquid mass ratio have certain effects on the leaching process of trace heavy metals. The leaching rate and amount of heavy metals remain at a very low level within the parameters explored in the experiment. In the typical operating parameters: the leaching rates of cobalt(Co),chromium(Cr),nickel(Ni) and lead(Pb) are lower than 0.10%,0.30%,0.05% and 0.10% for 30 min of sonication time, 25 ℃ of slurry temperature, and 1∶5 solid-liquid mass ratio. Considering the implementation and operation cost of the technical system comprehensively, the suitable sonication time is 15-20 minutes, the slurry temperature is 40-50 ℃,and the mass ratio of solid to liquid is 1∶3-1∶5. By comparing the key alkali metal elements, sulfur and chlorine elements in the leaching solution treated by ultrasonic-assisted leaching and the residue, a large number of macro-soluble elements migrate into the filtrate, and the content of trace heavy metals is very low. It is of practical significance for the leaching solution to be used as fertilizer and soil regulator. Due to the leaching of soluble alkali metal salt and chloride, the content in the residue is reduced significantly, which is favorable for its use as the raw material of industrial building materials.

Key Words: biomass fly ash;ultrasonic;alkali metal element;heavy metal element;ultrasonic-assisted leaching

Abstract:

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Foundation: 山东省重点研发计划资助项目(2016GGX104005)

Authors: HAN Kuihua;LIU Wenyang;SONG Chuanlin;REN Ke;TENG Zhaocai;NIU Shengli;WANG Yongzheng;ZHU Yingquan;LONG Shenwei;School of Energy and Power Engineering,Shandong University;Shandong Engineering Laboratory for High-efficiency Energy Conservation and Energy Storage Technology & Equipment,Shandong University;Shandong Fengyuan Biomass Power Generation Co.,Ltd.;

DOI: 10.13226/j.issn.1006-6772.CE21042703

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