Cement Based Solidification/Stabilization for Remediation of Contaminated Sites
As a result of the remediation of a former steel mill, 50,000 metric tonnes of leachable hazardous waste was recovered. The sources of the waste were from on-site settling ponds used for containment of electric arc furnace dust. This dust was generated as result of the melting of scrap metal used in the steel making process. Pockets of the waste existed in relatively pure form. Some of the waste was intermixed with native soils. Electric arc furnace dust is a listed hazardous waste having high concentrations of numerous metals The waste was sampled and determined to have leachable concentrations of metals that exceeded regulatory limits.
Brent Isfeld, P. Eng, President of BIRCO Environmental Services Ltd. decided that the solidification/stabilization (S/S) process would be the most effective and economical treatment solution for this waste. The result — a stable, non-hazardous material with leachability characteristics well below detection limits.
The S/S process reduced leachable metals to levels well below the detection limit of the laboratory equipment used for this analysis.
|Contaminant||Untreated||Regulatory Limit||After Treatment||% Reduction|
|Cadmium||1.2 mg/L||0.5 mg/L||<0.05 mg/L||-98%|
|Lead||14 mg/L||5 mg/L||<0.1 mg/L||-99%|
|Zinc||250 mg/L||500 mg/L||<0.05 mg/L||-99%|
What is Cement-Based S/S?
Solidification/stabilization (S/S) is a widely used treatment for the management and disposal of a broad range of contaminated materials and wastes – particularly those contaminated with substances classified as hazardous in the United States. The treatment involves mixing a binding reagent into the contaminated substance. This process protects human health and the environment by immobilizing contaminants within the treated material, preventing them from migrating to plants, animals and humans.
S/S treatment has been used to treat radioactive wastes since the 1950s and hazardous wastes since the 1970s. S/S continues as a cornerstone treatment technology for the management of radioactive and hazardous wastes, as well as site remediation and Brownfield redevelopment. The U.S. Environmental Protection Agency (EPA) considers S/S an established treatment technology. EPA has selected S/S treatment for 24% of its Superfund source-control remedial actions.
How S/S Works
S/S treatment involves mixing a binding reagent into the contaminated substance. Although the terms solidification and stabilization sound similar, they describe different effects that the binding reagents create to immobilize hazardous constituents. Solidification describes changes in the physical properties of a contaminated substance. The desired changes usually include an increase in compressive strength, a decrease in permeability, and encapsulation of hazardous constituents. Stabilization refers to chemical changes of the hazardous constituents in the treated substance. The desired changes include converting the constituents into a form that is less soluble, mobile, or toxic.
Effects of Binding Reagents on Waste – Inorganic & Organic
Commonly used binding reagents include Portland cement, cement kiln dust (CKD), and a number of proprietary reagents. Portland cement is a generic material principally used in concrete for construction. This material is also a versatile S/S binding reagent with the ability to both solidify and stabilize a wide variety of wastes. Portland cement-based mix designs have been the most popular S/S treatments and have been applied to a greater variety of wastes than any other S/S binding reagent.
Cement is frequently selected for the reagent’s ability to:
- chemically bind free liquids
- reduce the permeability of the waste form
- encapsulate waste particles, surrounding them with an impermeable coating
- chemically fix hazardous constituents by reducing their solubility
- help reduce the toxicity of some contaminants
This is accomplished by bringing about physical changes to the waste form and, often, chemical changes to the hazardous constituents themselves. Cement-based S/S has been used to treat wastes that have either or both inorganic and organic hazardous constituents.
Due to the great variation of waste constituents and media, a mix of reagents should be designed specifically for each waste that is to be treated. Mix designs often include by-products or additives in addition to Portland cement. Fly ash is often used to capitalize on the pozzolanic effect of this material when mixed with hydrating Portland cement. CKD and slag have minor cementitious properties and are sometimes used for economy. Lime can be used to adjust pH or to drive off water utilizing the high heat of hydration produced by these S/S binders.
|Owner||Western Steel Ltd.|
|Engineer & Contractor||BIRCO Environmental Ltd.|