Cost effective remediation technologies are currently available to treat many of the hazardous materials which are risks to human health and the environment. On-site remediation technologies, EPA’s preferred option, will be evaluated from a technological view point and the advantages, disadvantages and costs will be discussed.

Regulatory Framework

Since the promulgation of the Resource Conservation and Recovery Act (RCRA) many industries have been required to comply with extensive solid and hazardous waste permitting and regulatory compliance issues. The mining industry, because of the Bevill amendment, has been exempt from many of the RCRA regulations until studies determine the need to regulate mining wastes. EPA’s initial studies identified potential RCRA mineral processing wastes as high volume-low toxicity wastes.

On-site technologies that are currently available to support the mining remediation needs includes but are not limited to:

  • stabilization/solidification;
  • soil wash/soil flush;
  • thermal distillation/vacuum retort;
  • pump & treat;
  • metal extraction;
  • centrifugation/filter presses/separation; and
  • bioremediation.

Alternative Remediation Technology for Mineral Processing waste

Solidification/stabilization technology are technical processes used where additives are employed to reduce the mobility and/or reduce the toxicity of pollutants such that the mineral can meet regulatory Best Demonstrated Available Technology (BOAT) testing assessment and Land Disposal Restricted (LOR’s) criteria. Solidification processes are also applied to improve handling and physical characteristics of the wastes, whereas, stabilization  methods are used to either decrease the ability of the material to transfer to another more mobile transfer medium or are used to limit the solubility of the material being treated.

The major limitation in solidifying waste using kiln dust occurs when the water content in the waste exceeds 10%. Laboratory tests suggest the toxic material, when moisture content is elevated, may not be effectively solidified or immobilized by the solidifying agent. Metals which have been problematic includes selenium and cadmium.

In-Situ Stabilization Technologies

In-situ stabilization is a new technology which can be used to stabilize materials that are contaminated with metals. The process injects a calcium carbonate slurry into a the contaminated fractured or coarse grained formation. The slurry is permitted to solidify and or stabilize thus minimizing the risks associated with materials leaching from the treated zone.

Material Washing Technology

Soil Washing is a recently developed technology for the on-site treatment and removal of a variety of organic contaminants from soils, sludges and sediments in a low temperature, aqueous-based system. Recent tests suggest the technology may be applied to remove and/or treat volatilve non-volatile metals, inorganic cyanides corrosive, oxidizers and reducers.

Although site-specific modifications are sometimes necessary, the basic process involves initial sizing (less than ¼ inch) of the contaminated material by standard crushing and screening equipment followed by water pulping to an approximately 20% -30 % solids slurry. The slurry is then allowed to react with non-hazardous reagents which are added to liberate the contaminant(s) from the solid particles. The liberated contaminant(s) are separated from the bulk slurry using the well-established process of froth flotation. Typical additives includes surfactants, detergents, chelating agents, pH adjusting materials and heat.

APS Soil Flushing-In-situ Remediation

Alkaline-Polymer-surfactant (APS) Soil Flushing is a method for the in-situ removal of petroleum hydrocarbons and liquid organic compounds from the soil. The alkaline agents/surfactants reduces the interfacial tension between the oil and aqueous phase fluids. The chemicals increase fluid viscosity which provides mobility control and improves “sweep efficiency” through the aquifer. The technique is effective in removing contaminants in the vadose zone from the ground surface down to depths exceeding 500 feet.

Counter Current Soil Wash Extraction Technologies

Soil “counter current” washing technologies are used to remove organics/volatile metals/non-volatile metals inorganic cyanides/corrosives/oxidizers and reduces contaminant constituents from soils. The technology utilizes similar material handling procedures as outlined in the previously described soil wash technology section, however counter current soil wash procedures are used to effectively remove selected inorganic constituents.

Low Temperature Treatment

Thermal distillation is a treatment technology that uses the application of thermal energy to desorb, volatilize, separate and recover volatized constituents in contaminated soils, sludges and sediments. The process consists of feeding the contaminated soil to an indirect-fired rotary processor (kiln) operating at approximately 500°C under oxygen-deficient conditions. The organics and water constituents are volatilized from the soil, condensed outside the rotary processor and subsequently separated into individual organics/water phases. If possible the condensed materials are recycled or, if necessary, additional treatment is applied. The treated soil solids, after cooling, are usually returned to their source of excavation.

Vacuum Retort-Thermal Distillation

Vacuum retorting is a technology used in conjunction with the thermal distillation processes where excessive temperatures may adversely induce unwanted reactions during the thermal removal of the organic constituents from the waste. The vacuum process is applied to remove the volatilized non oxidized contaminant (PCB’s, chlorinated hydrocarbons, mercury etc) where the off gases are condensed, and recovered for further processing.

Pump and Treat

In most instances, hydrocarbon recovery using pumping systems alone will not meet or address regulatory or statutory issues. During the evaluation phase, contaminated saturated and unsaturated zones are characterized in regard to geochemical and physical properties which may adversely affect the implementation of a cost effective pump and treat system. An example of geochemcial issues which may affect design are related to whether the contaminant is dissolved, a dense non-aqueous phase (DNAP) or light non-aqueous phase (LNAP’s) contaminant.

Centrifugation/Separation

Centrifuge technology is designed to typically treat refinery sludges and oily wastes with solids content up to 30 percent weight and up to 60% by weight oil. Generally these waste streams can be categorized as sludges, dissolved air flotation (DAF) sludges, tank bottoms and miscellaneous mixtures of oil, water and solids. Historically, many of these wastes have been treated using land farming techniques and in other instances the waste streams have been dewatered using vacuum rotary drum filters, plate and frame filter presses or decanter type, low gravity (G) centrifuges.

implementing cost effective on-site remediation technologies for mineral processing wastes