Mass balance of silica at a Canadian deinking plant

Soluble sodium silicate is added to deinking processes to enhance ink removal, stabilize hydrogen peroxide, improve ink collection and flotation selectivity. Silicate can interact with deinking, papermaking and or water clarification chemicals to enhance their performance. To better understand and quantify, the distribution and over-all impact of soluble silicate within a modern newsprint recycling plant, a comprehensive mass balance of both soluble and insoluble silicate was completed using an enhanced microfiltration technique. Significant interaction of soluble silicate with calcium soap collector chemistry was inferred from the flotation cell mass balance data. As much as 75% of the added liquid sodium silicate eventually becomes insoluble within the process and leaves the Gatineau recycling plant, primarily with the finished paper and various solid reject streams.