Characteristics of ammonia-soda residue and its reuse in magnesium oxychloride cement pastes

Ammonia-soda residues (ASR), by-products from ammonia-soda factories, inevitably cause severe water pollution and soil contamination due to their strong alkaline features and polluting elements such as magnesium. The current recycling efficiency of these residues is quite low, only 3-4% in China, which calls for urgent improvement. This study focuses on the feasibility of reusing ASR in magnesium oxychloride cement (MOC) products. Initially, characteristics of ASR including physical/chemical properties were investigated. Then, impact of ASR on the fluidity and mechanical performance of MOC pastes were experimentally researched and analyzed according to microstructure observations. Results show that ASR is generally characterized with small particle size (95.8% <30 mu m) and high specific surface area (598.3 m(2)/kg). The main components of ASR tested are CaCO3, gypsum, Mg(OH)(2) and CaCl2 center dot 2H(2)O. When added in MOC pastes, ASR decreases the flowability and strength but accelerates the setting process. The free deformation of the composite is found largely increased in the presence of over 20 wt% ASR. Herein, MOC pastes with 10 wt% ASR exhibited reasonable strength and moderate expansion ratio as per corresponding product codes. Technical route of reutilizing ASR in MOC was found rational and feasible, since Mg in ASR causes little adverse effect on MOC pastes. To be noticed, consumption of the residues might be further improved if the expansion of ASR-MOC is effectively mitigated. (C) 2021 Elsevier Ltd. All rights reserved.