Progress in the study of the basic properties and engineering applications of alkali residue

Alkali residue is a byproduct of the ammonia-soda process used to produce soda, characterized by high output, low utilization, high moisture content, high porosity, and small particle size. These characteristics result in large-scale accumulation of alkali residue, severely hindering the development of the soda industry. There is an urgent need to accelerate the large-scale application of alkali residue. This article provides a comprehensive review of the research findings and recent advancements in the basic properties and engineering applications of alkali residue. The results indicate that alkali residue has a complex composition, with CaCO3 as the dominant mineral, accounting for 32.52% to 64%. Alkali residue is classified as general industrial solid waste, with heavy metal content meeting environmental standards. It can be used to improve bioleached heavy metals-laden sediment, sludge, clay, expansive soil, contaminated soil, shield tunneling slag, weathered mudstone, coal gangue, and backfill materials, or to prepare alkali residue-based soil and composite cementitious materials. However, current alkali residue application methods suffer from low consumption of alkali residue, limited application scenarios, inability to solidify Cl-, potential corrosion of steel reinforcement, and risk of secondary pollution. The author systematically investigates the basic properties of alkali residue from Lianyungang and proposes a method for producing alkali residue-based lightweight soil (A-LS) by combining alkali residue, cement, and granulated blast furnace slag (GGBS). A-LS offers several advantages, such as high strength, low density, excellent durability, simple production process, high efficiency, and low cost. With a 28d compressive strength of 0.96-4.27 MPa, A-LS is suitable as subgrade filling. Alkali residue content reaches 87.01-164.35 kg/m3, facilitating large-scale disposal and high-value utilization of alkali residue.