Newcomer’s introduction: Directions for the comprehensive utilization of ion-exchange membrane caustic soda sludge

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Based on the content in the salt sludge, the level of soluble salts resulting from saturated saline water limits the possibilities for the comprehensive utilization of this salt sludge. Let’s explore the utilization of salt sludge: An analysis was conducted on a sample of salt sludge produced from sea salt using a plate and frame filter press. The moisture content in this salt sludge was around 35%, while the proportion of insoluble substances exceeded 52% (calcium carbonate accounted for 30%, with magnesium hydroxide making up 14% and silicon dioxide 8%). The sodium chloride content was 13%. Before plate and frame filtration, it is possible to reduce the sodium chloride content by 0.5% through two rinsing steps; this method is already in use in other industries. According to the \"Standards for Pollution Control of Storage and Landfilling of General Industrial Solid Wastes\" (GB 18599-2020), salt sludge belongs to Category I general solid waste. Once the soluble salts are reduced, it can be used as a subgrade or filler without posing any hazards. The following are the regulatory provisions: 8. Requirements for filling and backfilling in terms of pollution control 8.1 General industrial solid waste of Category I can be filled or backfilled through the following methods: a) Fly ash can be used for filling or backfilling in the voids resulting from coal mining ； b) Coal gangue can be used for filling or backfilling in voids such as coal mining shafts and pits ； c) Tailings, mine waste rock, etc. can be filled or backfilled into voids such as mines and shafts in the original ore mining area. 8.2 For Category II general industrial solid wastes, as well as Category I general industrial solid wastes that do not meet the requirements for filling or backfilling outlined in Article 8.1, an environmental baseline survey shall be conducted prior to any filling or backfilling activities. An environmental risk assessment shall also be carried out in accordance with relevant standards such as HJ 25.3, with a focus on assessing the risks of environmental contamination to groundwater, surface water, and the surrounding soil, to ensure that such environmental risks remain acceptable. After the filling or backfilling activities are completed, long-term monitoring of the soil, surface water, and groundwater that may be affected should be carried out based on the results of the risk assessment, with monitoring conducted at least once a year.