Chemistry of unit operations in paper deinking mills

Unit operations in paper deinking mills encompass a range of mechanical and chemical processes. Pulping begins the process and is used to convert wastepaper into dispersed cellulose fibers. Pulping, kneading, and dispersion are unit operations in which ink is detached from cellulose fibers and the size and geometry of the dispersed ink adjusted for efficient removal in other unit operations. These unit operations include washing, flotation, screening, and mechanical cleaning. Additional unit operations such as bleaching, refining, and fractionation are used to impart the desired optical and physical properties to the recycled paper. The choice and sequence of unit operations is determined by the types of wastepaper being processed, the types of paper products being produced, and economic factors. Other unit operations critical to efficient and environmentally responsible mill operation include process water treatment and sludge handling.