With rapid industrial development, soil contamination has become increasingly prominent. Organic pollutants, heavy metals, and combined contamination pose serious threats to ecological environments and human health. As an efficient and stable strong oxidizing agent, sodium persulfate has been widely used in soil remediation due to its unique oxidation properties, making it one of the core agents in chemical oxidation remediation technologies. Its primary mechanism involves the activation to generate highly reactive sulfate radicals, enabling the degradation and immobilization of contaminants in soil. It is suitable for both in-situ and ex-situ remediation of various contaminated sites.
I. Core Principles of Sodium Persulfate in Soil Remediation
The chemical formula of sodium persulfate is Na₂S₂O₈. It has a strong oxidation capacity, with a standard redox potential of 2.01 V. Upon activation by specific methods, it generates sulfate radicals, which have an even stronger oxidation potential of 2.5–3.1 V, capable of effectively breaking down stable chemical structures of pollutants.
Activation of sodium persulfate is a critical step in the remediation process. Common activation methods include thermal activation, transition metal activation, alkaline activation, and combined activation. The activation reaction can be expressed as: S₂O₈²⁻ decomposes under heat, Fe²⁺, alkali, or light to form two SO₄⁻· radicals. The generated sulfate radicals rapidly degrade organic pollutants in soil, oxidizing hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), pesticides, and other organic contaminants into carbon dioxide, water, or small non-toxic molecules, thereby fundamentally eliminating the hazards of organic pollution.
In addition to degrading organic pollutants, sodium persulfate can also immobilize certain heavy metals. This is achieved by altering the valence state of metals through oxidation. For example, highly toxic As³⁺ is oxidized to As⁵⁺, and Cr³⁺ is oxidized to Cr⁶⁺ (note: Cr⁶⁺ is more toxic than Cr³⁺; subsequent stabilization treatment, such as reaction with lime to form insoluble chromates, is required). These oxidized heavy metals form insoluble salts, reducing their mobility and bioavailability in soil and minimizing contamination of soil ecosystems and groundwater.
II. Types of Soil Pollutants Suitable for Sodium Persulfate Treatment
The oxidation characteristics of sodium persulfate make it suitable for treating various soil pollutants, including organic contaminants, heavy metals, and combined contamination. It shows particular advantages in remediating co-contaminated soils.
For organic pollutants, sodium persulfate effectively treats petroleum hydrocarbons, PAHs, polychlorinated biphenyls (PCBs), organochlorine pesticides, dyes, antibiotics, and others. These pollutants are commonly found at gas stations, chemical plants, coking plants, and similar sites, where long-term accumulation degrades soil quality. Sodium persulfate, through radical oxidation, can completely degrade these pollutants and reduce their environmental risks.
For heavy metals, sodium persulfate mainly targets variable-valence metals such as arsenic, chromium, and mercury, focusing on their stabilization through valence transformation. It should be noted that its effectiveness in heavy metal remediation is largely limited to variable-valence metals. For stable-valence metals like lead and cadmium, the remediation effect is limited, and other techniques may need to be combined.
For co-contaminated soils, especially those at industrial sites, gas stations, and smelters, sodium persulfate is particularly effective. These sites often have complex contamination that is difficult to treat with a single technology. Sodium persulfate can simultaneously degrade organic pollutants and immobilize some heavy metals, offering an efficient solution for co-contaminated soil remediation.
III. Activation Technologies for Sodium Persulfate
The activation efficiency of sodium persulfate directly determines the effectiveness of soil remediation. Currently, four main activation technologies are commonly used, each with different conditions and characteristics. The choice depends on soil contamination levels and remediation goals.
Transition metal activation is one of the most widely used methods. Common transition metals include Fe²⁺, Fe³⁺, Cu²⁺, zero-valent iron, and nano-zero-valent iron. Among these, Fe²⁺ is the most commonly used activator due to its low cost and high activation efficiency. This method enables efficient activation at room temperature, but Fe²⁺ can excessively consume the oxidant, so dosage must be carefully controlled.
Thermal activation involves heating sodium persulfate to decompose it and generate sulfate radicals, with an optimal temperature range of 40–80°C. This method requires no additional chemicals and produces no secondary pollution. It is suitable for deep, low-permeability soils, but the heating process is energy-intensive, increasing remediation costs.
Alkaline activation is achieved by adjusting the soil pH to above 10 using alkaline reagents such as NaOH or CaO, which promote the activation of sodium persulfate. This method is simple to operate and has low costs. However, excessive use of alkaline reagents can lead to soil salinization and alkalization, affecting subsequent land use.
Combined activation integrates two or more activation methods, such as metal-thermal, metal-alkaline, or biochar-loaded nano-zero-valent iron activation. This approach achieves synergistic effects, reducing energy and chemical consumption while improving remediation efficiency. However, the process is more complex and requires higher operational expertise.
Post time: May-18-2026
