MBS is an EPA "SITE" (Superfund Innovative Technology Evaluation) program
technology, proven successful at the Midvale Slag Superfund site and on dozens of other
commercial applications. It provides simple, environmentally sound and cost effective
stabilization of heavy metals contamination. MBS effectively stabilizes all RCRA and UTS
metals and, with minimal reagent addition will permanently reduce the leachability of
metals in soil, sludge, slag, baghouse dust and ash to levels significantly below
regulatory limits. Heavy metals are chemically transformed into their metallic sulfides (a
metal's most insoluble form). The processed material is pH balanced, non-hazardous, and
unchanged in physical characteristics. In addition to the TCLP test, MBS has been
subjected to and passed other regulatory methods such as SPLP, SWEP, CAL WET and the
Humidity Cell and MEP long term stability tests.
MBS on-site operations may be completed either ex-situ or in-situ using standard
mixing equipment. MBS is proven for wastes classified as D004 through D011, as well as
K-listed wastes. MBS has effectively treated sludges, filter-cake, slag, paint chips, auto
fluff and various types of clay, soil, gravel and sand.
Solucorp maintains several mobile treatment systems that can be brought to your
site and set up within a matter of hours or days, depending on project size. Processing
rates range from 25 tons per hour to more than 250 tons per hour. Waste material is
screened and crushed to 2" or less in diameter. The waste is then blended with MBS
powdered reagents in a closed hopper pugmill system. Water may also be added at the
pugmill to increase moisture content to 15% to 20% and to promote uniform mixing. Treaded
soil exits the pugmill on a conveyor and is stockpiled.
MBS powdered reagents can be applied using traditional tilling methods by blending
reagents into the soil with appropriate equipment. Powdered reagents are stored in bags or
various sized silos with variable off loading augers. Water may be necessary to enhance
dispersion of reagents throughout the matrix being processed. After the reagents and water
have been applied to the surface and permeated the ground, soils are mixed to homogeneity
to a depth of up to two feet with either a backhoe, rototiller or other tilling/discing
equipment without any excavation of material. MBS can also be applied in a slurry form.
The MBS process can easily be integrated into a manufacturing line to stabilize a
heavy metal waste so it can be classified as non-hazardous. This means a safer facility,
lower insurance, compliance, training and disposal costs. The MBS in-line treatment unit
design is typically a simple mixing system, such as a pugmill. This system can be placed
in various locations on the production line, with the optimal location based on factors
such as: regulatory compliance issues, feed rate, material handling requirements and
others. Solucorp's engineering staff will customize a system to best capitalize on the
specific conditions present at your facility.
MBS PROCESS CHEMISTRY
In the MBS process, an inorganic sulfide reacts with the metal compounds in the
waste, converting leachable metallic ions into non-leaching molecules. A proprietary
reagent is used to minimize or completely eliminate hydrogen sulfide off-gassing, and to
provide long-term buffering capacity. An additional reagent is utilized to inhibit
MBS is composed of three or four reagents which are utilized
in proportions established by Solucorp's benchscale treatability study. These reagents are
normally provided as a single dry blend. The benefits and superiority of the MBS
stabilization system as compared to cement, lime, phosphate and other mineralization
systems are seen in the fact that metal sulfides are known to be much more stable and to
exhibit much lower solubilities. Reagent additions are very low, usually in the range of
2% to 5% by weight of waste, and the increase in volume of the waste attributable to
stabilization is usually less than 3%. In some cases, a volume reduction will occur.
The physical characteristics of MBS treated wastes are not changed by the process.
The treated wastes appearance will be basically unchanged. Additionally, there is no
curing time, as the MBS chemical reaction occurs immediately. Unconfined compressive
strength may be slightly increased and permeability may be slightly reduced. Moisture
content should be near optimum, yielding a treated soil which is ideal for use as contour
or fill. Unlike other technologies, since physical characteristics are unchanged, material
handling is easier.
Conventional cementitious stabilization systems rely heavily on pH control, and
these systems are usually evaluated using EPA's TCLP as the criterion for measuring the
success of the process. TCLP analysis is conducted using a buffered acid as the leaching
medium to evaluate the potential for leaching under worst case acid conditions.
Cement-based systems are strongly alkaline, so they can overpower the acid used in a TCLP
test and complete the leaching process in a mildly alkaline environment.
The MBS process has been developed to avoid the potential
leaching problem of cement-based systems. The leaching characteristics of the metal
sulfides that are formed are not pH sensitive. Final pH values in the TCLP extract, of MBS
treated wastes are often in the 5 to 6 range. This condition would result in failure of
cement-based systems. The tolerance of the MBS process to low pH has been demonstrated by
its resistance to leaching in the repetitive acid environment of the Multiple Extraction
Procedure (MEP) test.
SUMMARY & CONCLUSIONS
MBS is the most effective system to chemically alter the form of heavy metal
contaminants into a non-hazardous, stable compound. The simplicity of the MBS process
combined with its modular / transportable design and fully enclosed operational system
(preventing the release of contaminants or secondary wastes), provides lower operating
costs, enhanced safety and reduced emissions / secondary wastes.
The inherent ability of MBS to transform hazardous
contaminants into non-hazardous, insoluble compounds can facilitate on-site disposal of a
variety of wastes. The MBS process can also be easily integrated into a manufacturing
line. The result is a safer site or facility and significantly reduced liability.
When off-site disposal is necessary, MBS requires much less
reagent by weight than conventional processes resulting in a waste with minimal volume
increases. This significantly reduces storage, off-site transport and disposal costs.