A Study on the Adsorption of Methylene Blue by Acid-Modified Coal Measures Kaolin

Abstract

In this paper, coal measure kaolin after flotation decarburization was made into an adsorbent by ball milling and acid modification to absorb methylene blue in water, achieving the treatment of waste with waste. The objective of this paper is to expand the application of coal measure kaolin, reduce its stock, and lower the raw material cost of adsorbents while treating wastewater containing methylene blue. The optimum milling time, acid boiling conditions, and adsorption conditions were investigated. Furthermore, the adsorption mechanism was investigated by kinetic calculation. The results show that the optimum milling time is 7 h. Relatively good acid modification conditions include a boiling temperature of 100 °C, a stirring time of 135 min, a stirring speed of 1000 r·min−1, and a concentration of hydrochloric acid of 8 mol·L−1. When 0.05 g of flotation kaolin adsorbent was used to adsorb the solution with pH 12 and a methylene blue concentration of 100 mg·L−1, the optimal adsorption conditions were a 38.05 °C adsorption temperature, a 160 r·min−1 stirring speed, and a 31.02 min stirring time. Under these optimal conditions, the adsorption quantity reached 39.92 mg·g−1. The adsorption process involves physical adsorption and spontaneous adsorption. The adsorption type is known as the quasi-second-order adsorption kinetic model. The adsorption form is heterogeneous adsorption in which a monolayer and a multi-molecular layer coexist.