Key Takeaways & Executive Findings
- •• • PCA classification of waste salts into three types (sodium sulfate, sodium chloride, high-complexity mixed) enables tailored resource utilization pathways; sodium sulfate type (Q1, Q4, Q5, Q6) and sodium chloride type (Q2) are primary targets for recycling, while high-complexity mixed salts (Q3-A, Q3-B, Q7) require advanced treatment due to main salt content ≤60%. • • Total organic carbon (TOC) in waste salts ranged from 707.9 to 7,737.9 mg·kg⁻¹, with benzo(a)pyrene concentrations frequently exceeding GB 5085.3 limits, indicating significant organic contamination that must be addressed via advanced oxidation or thermal treatment before reuse. • • The park generated 32.6×10⁴ t of waste salt in 2023, with 90% classified as general industrial solid waste and 10% as hazardous waste; among general industrial solid waste salts, coal chemical waste salt accounted for 85%, and among hazardous waste salts, over 70% originated from coal chemical processes, underscoring the scale and urgency of management. • • Resource utilization potential is limited by pollutant composition and stability; for sodium sulfate and sodium chloride type salts, advanced oxidation and crystallization purification are required to meet product standards, while high-complexity mixed salts currently rely on harmless treatment (pyrolysis, oxidation) to reduce environmental risk, with long-term need for efficient separation technologies.
Abstract
Coal chemical industry waste salt, generated from high-salinity wastewater treatment, poses a bottleneck for green transformation under the 'dual carbon' strategy due to its low value and high complexity. This study investigated a typical coal chemical industrial park in Northwest China, using principal component analysis (PCA) on actual waste salt samples to identify pollutant characteristics and assess resource utilization potential. Results showed total organic carbon (TOC) ranged from 707.9 to 7,737.9 mg·kg⁻¹, with benzo(a)pyrene concentrations frequently exceeding the limits of the 'Identification Standards for Hazardous Wastes' (GB 5085.3). Hardness ions and metal ions also surpassed relevant product standards. PCA classified the waste salts into three types: sodium sulfate type, sodium chloride type, and high-complexity mixed salt, each corresponding to distinct resource utilization pathways. The study proposes differentiated technical routes based on PCA classification, providing a feasible reference for classified management and technology selection. This research supports the national policy of 'harmless pretreatment + resource utilization' for waste salt, contributing to green and high-quality development of the coal chemical industry.
1. Introduction
The coal chemical industry is integral to China's energy system but is characterized by high water consumption. With the implementation of the 'Water Pollution Prevention Action Plan' and 'near-zero emission' policies, enterprises have adopted evaporation crystallization to treat high-salinity wastewater, generating substantial waste salt. This waste salt often contains refractory organics such as tar and polycyclic aromatic hydrocarbons (PAHs), as well as heavy metals (Pb, Cr), particularly in large industrial parks where multiple processes coexist. The centralized treatment of wastewater results in waste salt that is a complex mixture of pollutants, making source tracing difficult and posing significant environmental risks. For instance, a study in Jiangxi found organic content up to 38.6% in waste salt, necessitating wet oxidation. In water-scarce northwestern regions, complex water quality further complicates resource utilization. Current research predominantly focuses on single-source waste salt or idealized treatment conditions, lacking a holistic understanding of real industrial park waste salt, leading to a mismatch between technology selection and actual needs.
Existing resource utilization pathways are constrained by pollutant types, compositional stability, and process adaptability. For example, a Shandong enterprise successfully treated waste salt from glycerol-based epoxy propane production via catalytic oxidation, enabling reuse in ion-exchange membrane caustic soda. However, for mixed waste salt from industrial parks with fluctuating composition, enterprises face a 'dare not use' dilemma due to inadequate characterization. Therefore, identifying characteristic pollutants and assessing resource utilization potential at the park level is critical for implementing the 'harmless pretreatment + resource utilization' model. This study addresses this gap by analyzing waste salt from a coal chemical industrial park in Northwest China, providing a scientific basis for classified management and technology selection, thereby promoting green and high-quality development of the coal chemical industry.
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YANG Jun, HE Yi, LIU Yanping, WANG Nianxi, ZHOU Tianlai, LIU Guoliang, ZHENG Yang (2026). Characterization of Pollutants in Coal Chemical Industry Waste Salt and Its Resource Utilization Potential: A Case Study of a Coal Chemical Industrial Park in Northwest China. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202508021
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Frequently Asked Questions
What are the key pollutant parameters that determine the classification of waste salt types, and how do they influence the choice of resource utilization technology?
The classification is primarily based on PCA of pollutant profiles, including TOC (707.9–7,737.9 mg·kg⁻¹), benzo(a)pyrene concentrations (exceeding GB 5085.3 limits), hardness ions, and metal ions. Sodium sulfate and sodium chloride types have relatively lower complexity, allowing for advanced oxidation and crystallization purification to meet product standards. High-complexity mixed salts, with main salt content ≤60%, require more intensive treatment such as pyrolysis or oxidation to reduce environmental risk before any potential reuse.
How does the waste salt composition vary across different enterprises in the park, and what are the implications for centralized treatment versus on-site management?
The study analyzed 16 enterprises, with waste salt sources including coal gasification, liquefaction, and olefin production. Enterprises Q1–Q7 have on-site treatment processes, while Q8–Q16 discharge saline wastewater to downstream facilities. The composition varies significantly, as reflected in the PCA classification: Q1, Q4, Q5, Q6 are sodium sulfate type; Q2 is sodium chloride type; Q3-A, Q3-B, Q7 are high-complexity mixed salts. This variability necessitates a centralized approach for mixed waste streams, but also highlights the need for source-specific pretreatment to improve resource recovery efficiency.
What are the main technical bottlenecks in achieving resource utilization of high-complexity mixed waste salts, and what future research directions are suggested?
High-complexity mixed salts contain multiple pollutants and low main salt content (≤60%), making separation and purification challenging. Current methods focus on harmless treatment via thermal or oxidative processes to reduce toxicity, but achieving high-purity salt recovery requires advanced separation technologies such as selective crystallization or membrane processes. Future research should expand pollutant detection to include emerging contaminants and develop integrated treatment trains that combine advanced oxidation with efficient separation to enhance resource recovery.
How does the regional context (e.g., water quality, coal type) affect the generalizability of the PCA classification method to other coal chemical parks?
The study acknowledges that water source background and coal type are region-specific, which may limit the direct transferability of the classification to other regions like North China. The PCA method itself is adaptable, but the specific pollutant profiles and thresholds may vary. Therefore, multi-regional studies are needed to validate and calibrate the classification criteria, ensuring robust application across different coal chemical clusters.
What are the environmental and economic implications of the current waste salt management practices in the park, and how does the proposed classification improve sustainability?
Currently, most waste salt (90%) is disposed of in landfills, which is not sustainable and poses long-term environmental risks. The proposed classification enables targeted resource utilization: sodium sulfate and sodium chloride types can be purified for industrial use, reducing landfill burden and creating economic value. High-complexity salts still require disposal but with improved pretreatment to minimize risks. This approach aligns with the national policy of 'harmless pretreatment + resource utilization', potentially reducing disposal costs and environmental footprint.
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