Regeneration and recycling of lime component in complex processing of kaolin raw materials

Technological independence of the Russian aluminum industry has historically been constrained by compromises related to the domestic raw material base, which suffers from a shortage of high-quality bauxite and a reliance on low-quality aluminum raw materials. Several key issues remain to this day. One major ongoing challenge is improving the utilization efficiency of waste sludge, a by-product of alumina production generated during the processing of both traditional and low-quality aluminum raw materials. An advanced strategy for the utilization of silicate-calcium sludge from alumina production has been developed and implemented. This strategy specifically applies to processing nepheline-based raw materials and enables the production of a variety of by-products. There are, however, certain economic limitations that impact the production and market demand for these by-products. These financial constraints necessitate the development and optimization of technologies that can effectively regenerate and recycle the lime component present in the silicatecalcium sludge with the goal to facilitate the processing of different types of aluminosilicate raw materials. Relevant thermodynamic calculations indicate that carbon dioxide conversion of calcium orthosilicate is possible under atmospheric conditions, resulting in the release of lime and silicate components, regardless of the specific polymorphic modifications of orthosilicate and calcium carbonate involved. It has been established that calcium orthosilicate tends to become passivated by the products of chemical interactions. However, conditions for the conversion of γ-2CaO·SiO2, leading to the formation of aragonite and observed during the processing of kaolinite raw materials, have been shown to be more favorable. The study theoretically substantiates and experimentally confirms the influence of the degree of carbon dioxide conversion of calcium orthosilicate on the formulation of a two-component raw Portland cement mixture. It also demonstrates the potential for a significant reduction (up to 6.6 %) in the proportion of the sludge flow required to regenerate the lime component.