Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1998-03-20
2001-04-17
Walker, W. L. (Department: 1723)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S747300, C210S912000, C588S001000, C588S020000
Reexamination Certificate
active
06217775
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
This invention relates to the clean-up, stabilization, or treatment of soils, water, and waste forms contaminated with metals such as lead, cadmium, uranium, and zinc, for the purpose of reducing the amount of metals that are leachable or that can subsequently migrate into the environment or be available to biological organisms.
BACKGROUND—DISCUSSION OF PRIOR ART
Metals readily leach from contaminated soils, sediments, rocks, waste piles, trenches, pits, and contained bodies of water. These leachates serve as sources of metal contamination to the environment, especially adjacent streams and underlying groundwater zones. Efforts to mobilize and remove metals from the subsurface to below regulatory limits have not been successful because of the various intermediate solubilities and sorption properties that each metal and suite of metals exhibit under most environmental conditions.
Alternately, metals can be stabilized in place to prevent them from migrating or leaching into groundwater. Many chemical additives have been studied to immobilize metals in these situations, e.g., lime, phosphate rock, carbonate rock, fly ash, clay minerals, zeolites, and sulfur and iron compounds. The additives can be mixed in with the soil or waste, emplaced as a permeable reactive barrier in a trench to treat groundwater moving through the trench, or emplaced as liners around a waste form or a contaminated site to treat any leachate leaving the site or waste form. Other studies have focused on pretreatment to remove metals before disposal of waste or contaminated soils. Others have used encapsulation to prevent subsequent leaching, e.g., cementing contaminated waste or soil. All have met with various degrees of success under various conditions. None have been satisfactory from the perspectives of performance, widespread applicability to many conditions, and cost.
The groundwork for this field of science has been laid by previous studies in widely divergent disciplines, including 1) phosphate mineralogy and crystal chemistry (LeGeros, 1981; Nriagu, 1984; Skinner, 1987, 1989; Skinner and Burnharn, 1968; Wright, 1990a,b; Wright et al., 1990); 2) scavenging and sequestration of minor and trace elements, such as uranium, metals, and the rare earth elements, in natural phosphate deposits (McArthur et al., 1990); 3) remediation studies of lead systems (Ma et al., 1993; Ruby et al., 1994; Xu and Schwartz, 1994; Stanforth and Chowdhury, 1994; Chen et al., 1997); 4) the impact and accessibility of phosphorus fertilizers to crops (Adepoju et al., 1986); 5) natural analogues in metallic mineral deposits (Koeppenkastrop and DeCarlo, 1988, 1992); 6) phosphate diagenesis during the formation and evolution of phosphorite deposits (McArthur, 1985) and 7) the evidence of changes in the paleochemical evolution of oceans, atmospheres, and climates evidenced by metals, lanthanides, and actinides incorporated into fossil material (Wright et al., 1987a,b and 1990a,b).
Geochemists have long known that metal phosphate compounds are generally less soluble and more stable than other metal compounds. Methods have been studied that use inorganic phosphates added to contaminated soils, water or wastes in order to stabilize the metals in phosphate compounds. The phosphate can be in many forms including phosphate minerals such as apatite, calcium orthophosphate, the inorganic constituents that form many fertilizers, phosphate glass, or dissolved phosphate salts in water. Cody et al., U.S. Pat. No. 5,162,600, discloses a method of using inorganic phosphate to stabilize lead, but the inorganic phosphate compounds are less effective than biogenic phosphates and the patent referred only to treatment of lead-contaminated soils.
Additives can act in several ways. The additive often provides ions to solution that can sometimes combine with metals in solution to form new metal-containing solids that can precipitate. In addition, an additive can buffer the pH or other aspect of the chemistry to a degree that makes leaching of metals less likely or induces the precipitation of metals into a new solid, or induces adsorption of the metal onto an existing solid surface. The additive can sometimes adsorb metals onto its own surface. Some metals can also sometimes replace or exchange for other metals in the structure of the additive. All of these possible actions depend upon the chemistry and conditions of the situation and depend upon the additive used. The additive usually treats the leachate or metals in solution as they leave the contaminated material and encounter the additive, either as a solid or in solution. The additive is not actually treating the contaminated solid. Therefore, the leaching solution containing the metals must come into intimate contact with the additive in order to be treated. Therefore, the emplacement strategy depends upon many factors in each situation.
The performance of a phosphate additive depends upon the specific chemistry of the additive, e.g., whether it is phosphate made of calcium hydroxyapatite or phosphate rock made of calcium fluorapatite. Each has different properties with respect to metal immobilization and treatment. Also, apatite minerals can be carbonated or chlorinated to varying degrees which greatly alters the performance with respect to metal immobilization. Additionally, different phosphate sources have different starting concentrations of metals already in their structure, e.g., phosphate rock usually has high levels of strontium and barium which makes it less useful for metal treatment. Also, the initial porosity of the phosphate material, i.e., the amount of pore space in the solid and the resultant surface area available for reaction, is different for different phosphate sources. In fact, there are over 300 apatite minerals alone with different compositions, different properties and different reactivities. Only a few are ideal for metal immobilization and treatment. Previous common sources of phosphate for additives include phosphate rock, phosphate fertilizers, bone char from cows, and reagent grade phosphate chemicals such as calcium orthophosphate. However, these inorganic sources are not adequate for many applications, often exhibit low reactivities, and are either costly or not available in enough quantities for large field operations.
OBJECTS AND ADVANTAGES
Accordingly, this patent fulfills the need to find an inexpensive, highly reactive phosphate material that is available in large quantities for the purpose of metal remediation and stabilization in soils, water and waste forms. This material is fish bones and fish hard parts. Fish bones and fish hard parts include all bones, scales, connective tissue and materials composed primarily of phosphatic compounds. As opposed to inorganic phosphate compounds, fish bones and fish hard parts are highly reactive with respect to most metals and contaminated water under many environmental and waste conditions, and can be applied in many different ways to soil, water and waste forms to treat or stabilize metals in order to prevent or reduce subsequent leaching of metals out of the system. Because of the stabilization conferred by the presence of fish bones and fish hard parts in the system, the bioavailability of metals is also greatly reduced, e.g., ingestion by birds of metal-contaminated soil is less toxic if the soil has been mixed with fish bones and fish hard parts. The degree of bioavailability depends upon the species and the conditions, but bioavailability of metals is lessened by the presence of fish bones and fish hard parts, or by the previous treatment of the soil or water or waste by fish bones and fish hard parts.
The fish bones and fish hard parts always have various amounts of organics still associated with them, and the presence of organics in the fish bones and fish hard parts makes them different from all other apatite formulations. The presence of organics on the fish bones and fish hard parts confers advantages in many situations where organics are desirable, e.g., situations involving revege
Conca James L.
Wright Judith
Christensen O'Connor Johnson & Kindness PLLC
Walker W. L.
Ward Richard W.
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