Decommissioned old coking plant sites generally suffer from combined soil‑groundwater contamination. Polycyclic Aromatic Hydrocarbons (PAHs) are the representative persistent organic pollutants at such sites. Characterized by stable molecular structure, poor biodegradability, long‑term persistence, ecotoxicity and potential migration risks, PAHs are key regulated contaminants for soil remediation and land redevelopment of legacy industrial urban sites.
Among various remediation technologies, sodium persulfate chemical oxidation stands out for its high reagent stability, broad‑spectrum free‑radical oxidation performance and compatibility with aged recalcitrant contamination. It has become one of the vital technical solutions for PAHs pollution treatment at former coking plant sites. Fujian Zhanhua Chemical provides high‑quality sodium persulfate complying with field engineering specifications, delivering reliable reagent support for refined oxidation remediation of coking‑plant sites.
Ⅰ. Core Contamination Characteristics of PAHs‑Polluted Former Coking Plant Sites
Long‑term coking activities including raw‑material stacking, coking production, chemical‑product recovery and wastewater leakage continuously release organic pollutants such as PAHs. Decades‑long soil aging, solid‑liquid adsorption and pore retention have formed recalcitrant contamination patterns distinct from ordinary chemical‑polluted sites.
High proportion of high‑molecular‑weight PAHs with low natural degradability: Site contaminants are dominated by high‑molecular‑weight PAHs. These substances feature stable molecular structures and high chemical‑bond energy. They can hardly be degraded via natural biological metabolism or conventional soil washing, and persist in soil to pose long‑term contamination hazards.
Wide vertical contamination distribution bringing challenges for deep‑layer remediation: Seepage of coking‑process waste liquid and leaching of solid waste drive PAHs to migrate downwards through soil pores and fissures, creating cross‑layer contamination zones across shallow, intermediate and deep soil layers. Shallow‑layer pollutants may be re‑released under surface‑runoff disturbance, while conventional remediation reagents show limited penetration and fail to fully contact contaminated soil mass.
Prominent aging‑induced adsorption‑sequestration effect: Long‑term contamination enables strong binding between PAHs and soil organic matter, clay minerals and colloidal particles, generating large quantities of aged sequestered pollutants. Tight bonding between residual PAHs and soil particles makes it difficult for chemical oxidation to achieve required degradation efficiency.
Superimposed multi‑component combined contamination complicates remediation systems: Coking‑plant sites commonly feature combined pollution of “PAHs + petroleum hydrocarbons + heavy metals”. Organic and heavy‑metal fractions are mutually coupled. Single remediation mode cannot mitigate multiple pollution risks simultaneously, placing higher requirements on reagent versatility and process compatibility.
Ⅱ. Mechanism of Sodium Persulfate Oxidation Remediation Technology
Sodium persulfate is a robust long‑acting solid oxidant for In‑Situ Chemical Oxidation (ISCO) of soil. Its molecular structure contains stable peroxy bonds. Upon activation via thermal, alkaline or transition‑metal pathways, peroxy bonds cleave to generate high‑activity sulfate radicals (·SO₄⁻), together with derivative hydroxyl radicals (·OH), which effectively degrade recalcitrant PAHs.
The reagent exhibits stable performance in ambient‑temperature storage, transportation and field application, withexcellent water solubility. It is compatible with mainstream construction processes including in‑situ pressure injection and ex‑situ mechanical mixing. After being applied into soil, it diffuses evenly with pore water and comes into contact with free‑state, pore‑adsorbed and aged‑sequestered PAHs. The generated reactive free radicals break the stable molecular skeleton of high‑molecular‑weight PAHs, decompose cyclic organic structures, and gradually mineralize pollutants into low‑/non‑toxic intermediates, carbon dioxide, water and other harmless substances, thus reducing soil ecotoxicity and pollutant migration risks.
The reaction system features a wide applicable environmental range and is not overly restricted by soil pH matrix or soil texture. Under properly‑dosed engineering conditions, sulfate constitutes the major end product, with controllable secondary‑pollution risks. Sodium persulfate manufactured by Fujian Zhanhua Chemical has high purity and strictly‑controlled transition‑metal impurities, which prevents premature ineffective reagent decomposition caused by excessive impurities and guarantees remediation performance.
Ⅲ. Application Advantages of Sodium Persulfate Oxidation Technology
Targeting typical site features of former coking‑plant sites: recalcitrant aged PAHs, deep vertical distribution and combined pollution, sodium persulfate oxidation remediation demonstrates strong site adaptability and engineering value.
This technology delivers broad‑spectrum pollutant degradation capacity. It effectively disrupts adsorption restraints imposed by soil colloids and organic matter on PAHs, and achieves favorable degradation performance against aged residual high‑molecular‑weight polycyclic aromatic hydrocarbons, mitigating common problems such as residual exceedance and unstable remediation outcomes at coking‑plant sites. For field implementation, in‑situ operation avoids large‑scale earth excavation and soil transport, preserves original stratum structure to the maximum extent, generates minimal construction disturbance and imposes low impacts on surrounding environments. It is well‑suited for remediation projects of old coking‑plant sites within built‑up urban areas.
Benefiting from favorable water‑solubility, the reagent can be delivered via pressure‑injection processes to improve penetration and transport within soil pores. For geologic formations with proper permeability, it can cover contamination zones ranging from shallow to deep layers. Faced with widespread combined pollution at coking‑plant sites, the oxidation system modifies soil redox potential while degrading PAHs, which helps lower potential migration risks of associated heavy‑metal fractions and creates conditions for synergistic treatment of multiple pollutants. Supported by large‑scale production capacity, Fujian Zhanhua Chemical ensures continuous and stable reagent supply for various site‑remediation projects to facilitate efficient project execution.
Ecological remediation of legacy industrial coking‑plant sites is an essential component of land‑ecological restoration and urban land renewal. Efficient, eco‑friendly and highly‑adaptable remediation technologies hold the key to resolving site‑treatment challenges. Breaking through limitations of conventional treatment approaches, sodium persulfate oxidation remediation aligns with current low‑carbon and refined ecological‑restoration concepts, and provides a reliable technical pathway for complex sites with combined industrial contamination.