Solidification treatment of fluorine-containing sludge by composite Portland cement

Composite Portland cement was used to solidify fluorine-containing sludge and to prepare cement standard test blocks with different sludge content. The effects of fluorine-containing sludge content on the compressive strength, fluorine ion leaching amount, phase transformation and crystal morphology of test blocks were investigated. The results showed that when the fluorine-containing sludge content (mass fraction) was 10%, the prepared test block had the highest strength and low amount of fluorine ion leaching. The compressive strength of the test block after maintenance 28 d reached 22.2 MPa, which met the strength requirements of general cushion, foundation, floor and structure with little stress. The fluoride ion leaching amount of the test block with 10% fluorine-containing sludge under the action of groundwater and acid rain was 0.16 and 0.39 mg/L, respectively, far less than the standard limit of 100 mg/L of hazardous waste, indicating had high safety. Mechanism study indicated that the addition of fluorine-containing sludge accelerated the hydration rate of tricalciumaluminate (C3A) in cement, increased the formation amount of ettringite (AFt) in the early stage, and improved the early strength of the test block. © 2021, Editorial Office of FINE CHEMICALS. All right reserved.