FAQ about the proposed soil washing technology

22
Dec

Frequently asked questions about the  proposed soil washing technology

 

 

  1. Does technology remove only Pb from contaminated soil?

Response. Pb is the most ubiquitous and health-vise the most problematic metallic soil pollutant. Nevertheless EDTA is non-specific chelant and removes also Cd, Zn, Cu, Tl and other soil contaminating metals.

 

  1. EDTA acts non-specifically on soil metals. Does technology remove metallic micronutrients along with toxic metals?

Response.  Cu, Zn and Mn are micronutrients and in excessive concentration also soil pollutants which are removed by our technology. Our results indicate that other major soil metals: Fe, Al, Mg and Ca are not removed substantially.

 

  1. Does technology remove entire concentration of toxic metals from soil?

Response. No technique is able to quantitatively remove toxic metals from soil. Our technology removes up to 90% of toxic metal soil concentration. Removal efficiency depends on soil type (acidic or carbonate), means of pollution (air emissions or solid deposits) metal speciation (carbonates, sulfides/sulphates, oxides etc.) and bonding to the soil solid phase (to soil organic matter, to soil oxy-hydroxides). In any case our technology removes at least 80% of toxic metals bio-accessibility from soil into the simulated human gastro-intestinal solution.

 

  1. Technology removes major toxic metals from soil, what about other contaminating elements?

Response. As a part of the process our technology enables for efficient remediation by immobilization of frequent contaminating elements, such is As. 

 

  1. Soil washing technologies are characterized by production of large amounts of waste waters. How much waste waters are produced?

Response. None. Our innovative technology recycles all process (washing and rinsing) solutions in a closed process loop. No waste-waters are produced.

 

  1. What about gaseous emissions and other wastes?

Response. Our technology produces no gaseous emissions. The only waste produced is up to 1.5 kg of solid wastes per ton of remediated soil.  

 

  1. Are the produced solid wastes reusable?

Response. Disposal of small quantity of solid wastes represent bearable additional cost to remediation. There is also alternative for reuse. Metals absorbed on waste paper can be reclaimed after incineration and calcinated metal-oxides in a lime cake can be delivered to smelting plant.

 

  1. How much of the chelating agent, EDTA, technology recycles?

Response. Technology recycles at least 85% of EDTA. The lost EDTA must be resupplied. Most of lost EDTA is degraded during remediation processes and minor part of EDTA remains in soil despite of an extensive soil rinsing with cleansed rinsing solution and at the final rinsing step with drinking water. 

 

  1. EDTA is a low bio-degradable chelant. Could EDTA which remain in remediated soil cause secondary emissions?

Response. Potential residual emissions of EDTA and toxic metals are efficiently prevented by simple short-term maintenance of a neutral water balance in in situ deposited remediated soil (i.e. by shielding the soil in cases of excessive rainfall). Deposition of remediated soil on inexpensive permeable horizontal barrier containing Ca(OH)2 as reactive material could be applied as an additional measure of precaution.  

 

  1. Does EDTA-soil washing harm soils?

Response. Remediation does not reduce soil organic matter content, change soil pH nor impede other vital soil properties. However, conditions during EDTA soil washing reduce diversity and activity of soil fauna and flora. Simple revitalization by fertilization (i.e. with Mn) and amending soils with compost, inoculum of un-contaminated soil or soil extract normalizes soil microbial community composition and activity. Remediated soils are fully functional and support plant growth.

 

  1. Can remediated soil be used for safe vegetables production?

Response. Yes. Our results indicate that the Pb concentration in edible parts of vegetables produced on remediated soil is below values stipulated by EU legislature. Furthermore, our results prove that remediated soil provides all expected ecosystem services.       

 

  1. Are there other available similar soil remediation technologies?

Response. Our technology is the single commercially available technology which efficiently removes toxic metals from soils and sediments, recycles reagent and process waters, generates no liquid wastes, produces no emissions and preserves remediated soil as a natural resource. 

 

  1. Is technology suitable for remediation of large areas of contaminated land?

Response. Yes. Technology uses ex situ soil extraction in reactor and on site heap leaching of contaminated soil. Ex situ technology is suitable for rapid remediation of disperse patches of soil characteristic for urban gardens. On site technology enables remediation of contaminated farmlands and larger industrially contaminated areas.

 

  1. Question. How costly is technology?

Response. The total remediation cost (fixed, variable, depreciation, labor, profit etc.) is governed by the economy of scale. The discriminated material, energy and solid waste disposal cost amounts to up to 21 € per ton of remediated soil.  

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