Large quantities of contaminated soil can be prepared for thermal treatment by first processing the material mechanically: oversized fractions are screened out, foreign materials are sorted out, and the moisture content is reduced to a workable level. This pre-treatment is not an optional addition but a technical necessity to ensure the rotary kiln operates efficiently and consistently. The following sections answer the most important questions about soil pre-treatment prior to thermal desorption.
What requirements must contaminated soil meet before thermal desorption?
Contaminated soil must exhibit certain physical properties before thermal desorption: the particle size must not exceed a defined maximum value, the moisture content must fall within a workable range, and foreign substances such as metals, plastics, or coarse organic components must be largely removed. Only then can stable and efficient operation of the rotary kiln be ensured.
In addition, a precise characterization of the source material is required. Before delivery, the soil is analytically examined to determine the type and concentration of contaminants. This data forms the basis for approval for treatment and for setting the process parameters. Soils with highly variable properties or unknown contaminant composition must first be sampled and evaluated before they can be introduced into the treatment process.
How are large quantities of contaminated soil mechanically pre-treated?
The mechanical pre-treatment of large quantities of soil takes place in several successive steps: first, the delivered material is screened to separate oversized fractions. Subsequently, interfering substances such as reinforcing steel, films, or wood residues are sorted out. In further steps, the material may be crushed or homogenized before being fed into the thermal process.
For large remediation projects, stationary or mobile processing plants are used that combine screening machines, crushers, and conveyor technology. The mechanical-physical treatment serves not only to prepare the material for the kiln, but also for pre-sorting: materials that do not need to be or cannot be thermally treated are removed from the material stream at an early stage. This reduces costs and significantly increases process efficiency.
Suitable storage capacities are required for the interim storage of large quantities of material before and after processing. A structured interim storage facility makes it possible to control the material flow and absorb peak quantities from construction projects without interrupting ongoing treatment operations.
Why is the moisture content of soil critical for thermal treatment?
The moisture content of the soil is critical for thermal treatment because excessively wet material in the rotary kiln requires considerable amounts of energy to evaporate the water before the actual contaminant desorption can take place at the required temperatures. An excessively high moisture content reduces throughput, increases energy consumption, and can impair process stability.
Soils with a moisture content of more than 20 to 25 percent generally need to be dried or mixed with drier materials before thermal treatment in order to enable economical operation. Conversely, material that is too dry can generate dust and place a burden on emission control. The optimal moisture content lies within a range that allows uniform mixing in the kiln while keeping energy input controllable. The precise target value depends on the material composition and the specific contaminant profiles.
Which contaminants can be removed from soil by thermal desorption?
Thermal desorption can remove a wide range of organic and inorganic contaminants from soil. These include mineral oil hydrocarbons (MKW), BTEX compounds, phenols, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), per- and polyfluoroalkyl substances (PFAS/PFOS), dioxins and furans (PCDD/PCDF), cyanides, nitroaromatics, and numerous other chlorinated hydrocarbon compounds. Mercury (Hg) is also among the treatable contaminants.
Treatment takes place in the rotary kiln at temperatures of up to approximately 600 °C, depending on the material composition and contaminant load, under exclusion of oxygen. Under these conditions, volatile contaminants are driven out of the soil material and converted into the gaseous state. Poorly volatile compounds are thermally destroyed. The resulting exhaust gas then passes through a multi-stage purification process involving dedusting, thermal post-combustion, flue gas scrubbing, and activated carbon filters to reliably comply with statutory emission limit values.
Typical areas of application include decommissioned gasworks, former industrial sites, and contaminated areas of military or chemical facilities where complex mixtures of contaminants are present. More information on thermal soil treatment and the approved waste types can be found in the services overview.
What happens to the treated soil after thermal desorption?
After thermal desorption, a mineral material is produced that is largely free of organic contaminants. This treated material is analytically examined to document the contaminant levels following treatment. Depending on the analysis results and the applicable legal requirements, the material can then be sent for recycling or properly disposed of.
In many cases, the treated soil meets the requirements for use as a construction material, for example in road building or earthworks. This reduces the need for primary raw materials and closes the material cycle. If recycling is not possible, the material is disposed of in a suitable landfill. The decision on the further use of the material is made by the responsible company on the basis of the analysis data and in consultation with the competent authorities. A structured material flow management system ensures that all material fractions are transparently documented and properly handled.
When is thermal desorption the appropriate method for contaminated soil?
Thermal desorption is the appropriate method when contaminated soil contains volatile or semi-volatile organic contaminants that can be driven out of the soil material by heat, and when complete contaminant destruction or separation is required. It is particularly suitable for complex contaminant mixtures, high contaminant concentrations, or when other methods such as biological treatment are not sufficiently effective.
The method is particularly useful when large quantities of material need to be treated in a short time, for example in time-critical remediation projects or when areas need to be quickly released for subsequent use. Compared to landfilling, thermal treatment offers the advantage that contaminants are actually destroyed or removed, rather than preserving the problem in the long term.
Thermal desorption is not suitable for soils whose contaminants are exclusively inorganic in nature and do not exhibit volatile properties, for example in the case of pure heavy metal contamination without any organic co-contamination. In such cases, other methods of soil treatment or immobilization are more appropriate. The decision in favor of the right method requires a well-founded analysis of the source material.
How ARE Deutzen GmbH supports the preparation and thermal treatment of contaminated soils
ARE Deutzen GmbH supports civil engineering companies and industrial customers from the initial material characterization through to the final recycling or disposal of the treated material. The range of services covers all key steps in the process chain:
- Analytical assessment and approval of the source material
- Mechanical-physical pre-treatment to prepare material for the rotary kiln
- Interim storage of large quantities of material from ongoing construction projects
- Thermal treatment at temperatures of up to approximately 600 °C, depending on the material composition and contaminant load, under exclusion of oxygen
- Multi-stage exhaust gas purification to comply with all emission limit values
- Material flow management and documentation for all material fractions
- Coordination of recycling or landfill disposal of the treated material
With over 30 years of experience and more than 2.5 million tonnes of treated mineral materials, ARE Deutzen has the technical expertise and plant capacity to reliably handle even demanding remediation projects involving large quantities of material. Contact us to discuss your project and receive a concrete assessment for your soil quantities.