The Siallon microencapsulation process is applicable to the treatment of a wide variety of waste materials. The hydrocarbons that have been successfully treated and found to be amenable to treatment by microencapsulation include crude oil, gasoline, coal tars, creosote, lubricants, diesel fuel, jet fuel, PCBs, and refinery wastes.
The differences between many types of wastes are related not so much to the type of contaminant as to the physical form of the waste matrix. The treatments of pure crude oil, crude oil-contaminated soil, and crude oil sludge are all chemically similar; the differences lie in the physical form of the material to be treated and in how it is handled during treatment. The most important aspect of any Siallon treatment is that adequate mixing of the host material must be obtained during the application of the reagents. For materials differing in physical characteristics, it is obvious that different mixing equipment or methods are required.
For remediation of normal contaminated soil, a pug mill has been found to meet all of the requirements for efficient application of the Siallon process. A pug mill is simply a continuous mixer with twin side-by-side helical mixing blades. The pug mill is used in many industries for a variety of mixing and blending operations. The concrete industry and the mining industry are large users of pug mills. For the processing of Siallon-treated soil, the large throughput of a pug mill combined with the instantaneous reaction of the Siallon reagents makes the pug mill an ideal tool for remediation of small to large quantities of soil. Pug mills for soil remediation range in size from 15 tons/hr up to 200 tons/hr. At these rates the Siallon process becomes one of the most cost-effective remediation methods available.
Processing contaminated soil through a pug mill is a relatively simple operation. The soil is added to the pug mill hopper via a conveyor or auger system. As the soil enters the hopper, the Siallon emulsifier is applied by spray. Approximately halfway down the pug mill, the Siallon reactive silicate is added. The soil exits the pug mill after a 90-sec residence time and is ready for final disposition.
The pug mill is adjustable for mixing speed and residence time as well as flow rate and pressure of the spray-applied reagents. This allows a pug mill to easily be configured to treat many different contaminants, soil types, levels of contaminant, and various site conditions with the Siallon process.
For sludges or heavy clays of high moisture content, a ribbon blender is the most appropriate mixing equipment. Ribbon blenders are used in a wide variety of industries for mixing and blending everything from powders to pastes. The food, chemical, detergent, pharmaceutical, and paint industries all make use of this versatile mixer. These mixers come in watertight configurations for mixing pastes or fluids, which makes them ideal for use as a mixing system for sludges, tars, or other high water content materials.
The use of ribbon blenders for soil or sludge remediation with the Siallon process is a batch-type production. The mixer is charged with a known quantity of sludge and is then turned on. After 30 sec of mixing to ensure homogeneity of the mixture, the Siallon emulsifier is automatically sprayed into the mixer. This is mixed in for 2 min, after which the Siallon reactive silicate is automatically added. A further 2 min of mixing ensures that total reaction has taken place, and the treated soil is dumped through a bottom valve to a conveyor.
Ribbon blenders come in sizes ranging from 1 to 30 yd3 capacity, so processing 100 tons/hr of sludge is a simple matter. The watertight nature of the blender ensures that everything that comes out of the system is treated and encapsulated.
The use of these blenders provides for excellent QA/QC procedures as all of the processing parameters can be easily monitored or adjusted.
For soil remediation on specific sites where the contaminant has little or no volatile component, there is a large amount of debris or cobble in the soil, and there is sufficient space to lay out the contaminated soil in windrows, a tractor-driven soil-mixing machine has found application. The Dirt Witch is similar to equipment used for composting soil in its overall design. The differences are in the mixing blades, the spray system, and the control system. The equipment used for the application of Siallon reagents is modified to provide intimate soil mixing rather than the simple blending accomplished with composting machines. The mixing blades are L-shaped to provide maximum turbulence in the soil. Reagent is added from a bulk storage tank controlled by pressure settings and flow rate to provide the proper spray pattern and force of impingement on the soil particles. A tachometer is used to ensure constant mixing speeds, and a low-speed speedometer is used to ensure a constant mixing time on any given soil block.
There are several advantages to the use of this equipment for ex situ remediation. Only debris larger than 10 in. has to be removed from the soil. Processing rates are upwards of 100 tons/hr, depending upon site conditions. The equipment is simple and inexpensive, working off the power take-off of a standard tractor.
To remediate soil with the Dirt Witch, the soil is laid out in windrows on a plastic liner. The windrows are generally 6 ft high and 8 ft wide, the length of the windrow being governed by the site. The Dirt Witch moves through the windrow, mixing and adding the reagents in a sequential manner. In other words, it will make a complete pass mixing and applying the Sial-lon emulsifier and then a second complete pass mixing and applying the Siallon reactive silicate.
For on-surface or shallow-depth soil remediation, the use of a Bomag or similar type of mixing equipment has been found to be the most practical. These mixers are generally used for soil or sludge solidification, and the only modifications necessary are the addition of the reagent flow control and spray system. Their mixing depth is usually limited to 18 in., and their speed in applying Siallon materials is 1 mph on an 8-ft-wide path. This makes their use one of the most cost-effective and efficient methods of remediating large sites where the contamination is all within the top foot of surface.
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