Influences of alkaline oxidant on strength of cement-stabilized sludge

In order to eliminate the adverse effects of organic matter on the treatment of sludge with cement, the countermeasures to increase the strength of cement-stabilized sludge are put forward, including degrading organic matter, reducing thickness of double electric layers and maintaining pH value steadily. The potassium ferrate and sodium bicarbonate are used as the alkaline oxidant to treat the sludge with cement. Through the unconfined compressive strength tests, the influences of alkaline oxidant on the strength of cement-stabilized sludge are understood preliminarily. The solidification mechanism of alkaline oxidant is studied by means of the organic element tests, electrokinetic potential tests, specific surface area tests and SEM. The experimental results show that the unconfined compressive strength of cement-stabilized sludge can reach 1.536 MPa after curing for 7 days using the alkaline oxidant. The sodium bicarbonate maintains the cement-stabilized sludge in an alkaline environment with the pH value at 9 to 10 by neutralizing organic acids. Under this condition, the potassium ferrate can degrade organic matter effectively. Thus, the removal of the organic matter shell on the surface of clay particles is conducive to free SiO₂ and Al₂O₃ to dissolve into the pore solution, which promotes the formation of cement hydration products. Besides, the high valence ions in pore solution replacing the low valence ions on the clay particles surface lead to a decrease in repulsion between the successive diffused double layers and the flocculation of soil particles.