Patent Application
20070267343
HMP complexing is herein defined as reducing the solubility and thus bioavailability of heavy metal bearing particulates from air emission sources. The confirmation of leaching reduction can be determined by performing a suitable leaching test on the particulate and optional methods by physical evaluations of mineral formation under selective electron microscopy (SEM), x-ray diffraction (XRD) or chemical extraction techniques.
Heavy Metal Particulate (HMP) can be in a variety of molecular forms including elemental, anionic or cationic form. The most common molecular form of HMP from point-sources such as municipal solid waste refuse incinerators, wood incinerators, fossil fuel combustors, primary and secondary smelters, metal casting shops and foundries, shredders, steel mills and non-point sources such as highways, parking lots, and roofs are as an oxide, sulfate or chloride. Many HMP sources are in a molecular and physical form designed by the HMP generating facility environmental engineer to achieve large particle capture in APC filtration units. Such engineering does not include methods for HMP uncollected exposure control to receptors such as fish, humans, plant and crops uptake area, and animals. Soils and materials subjected to HMP deposition such as residential and crop field soils surrounding smelters and refuse incinerators can for example contain as high as 2500 ppm compositional lead and 50 ppm TCLP leachable lead from long-term constant air stack particulate emission deposition and accumulation.
Leach test conditions, as defined herein, include the conditions to which a material or soil impacted by HMP release and deposition is subjected during dilute acetic acid leaching (TCLP), buffered citric acid leaching (STLC), distilled water, synthetic rainwater or carbonated water leaching (US SPLP, Japanese and Swiss and SW-924). Suitable acetic acid leach tests include the USEPA SW-846 Manual described Toxicity Characteristic Leaching Procedure (TCLP) and Extraction Procedure Toxicity Test (EP Tox) now used in Canada. Briefly, in a TCLP test, 100 grams of waste are tumbled with 2000 ml of dilute and buffered acetic acid for 18 hours. The extract solution is made up from 5.7 ml of glacial acetic acid and 64.3 ml of 1.0 normal sodium hydroxide up to 1000 ml dilution with reagent water.
Suitable water leach tests include the Japanese leach test which tumbles 50 grams of composited waste sample in 500 ml of water for 6 hours held at pH 5.8 to 6.3, followed by centrifuge and 0.45 micron filtration prior to analyses. Another suitable distilled water CO2 saturated method is the Swiss protocol using 100 grams of cemented waste at 1 cm3 in two (2) sequential water baths of 2000 ml. The concentration of heavy metals and salts are measured for each bath and averaged together before comparison to the Swiss criteria.
Suitable citric acid leach tests include the California Waste Extraction Test (WET), which is described in Title 22, Section 66700, “Environmental Health” of the California Health & Safety Code. Briefly, in a WET test, 50 grams of waste are tumbled in a 1000 ml tumbler with 500 grams of sodium citrate solution for a period of 48 hours. Leachable heavy metals, contained in the waste, then complex with citrate anions to form lead citrate. The concentration of leached metals are then analyzed by Inductively-Coupled Plasma (ICP) after filtration of a 100 ml aliquot from the tumbler through a 45 micron glass bead filter. A WET result of ≧5 ppm lead for example will result in a waste determination as hazardous in California.
According to the methods of the invention, HMP can be complexed by contact with at least one complexing agent and water at sufficient dosage, temperature, turbulence and duration to allow for complexing of relatively soluble heavy metals to relatively insoluble complex forms prior to emission. The amount of complexing agent and water incorporated with the HMP will be that which is effective in reducing the leaching of heavy metals from the particulate as needed, for example to a level no more than 5.0 ppm lead, as determined in an EPA TCLP test performed on the particulate or material receiving the particulate as set forth in the Federal Register, Vol. 55, No. 126, pp. 26985-26998 (Jun. 29, 1990), or other leaching test relating to receptor exposures, digestive capacity and or bioaccumulation. Regardless of the receptor, complexing HMP to a less soluble form will directly reduce exposed receptors and environmental health and biological impact risks.
The complexing agent and water can be incorporated within or applied to the HMP by in-line slurry injection or wet chemical injection prior to or after HMP capture units, bath contact, spray, or other application means. Depending on the HMP discharge system such as tall air exhaust stacks (such as Good Engineering Practice (GEP) height required under the CAA at new and modified point air emission sources) application of HMP complexer and water can be added to the discharge side of the APC devices, thus avoiding possible chemical-physical complications with augmentation of the APC unit operation with a HMP complexer. As many APC systems are precisely designed for the process feed character and chemistry, post-collection HMP complexing as a polishing unit may be best suited for existing control units. It also remains possible that the HMP complex agent may be optimally applied during formation of the heavy metal particulate prior to emission in the production process such as within the furnace firebox, within scrubbing acid gas application units, within primary shredders, and at other locations permitting introduction of complexers and water to convert particulate metals to non-leachable complex form(s). Given that the particulate surface is the primary exposure area to the environment and that the complex surface will likely reduce or significantly retard diffusion from the particulate core, the stabilization of the HMP surface alone is offered as one optional control which also provides for use of field spray post-stack air pollution control devices that can be applied to existing operations not utilizing heavy metal complexing during production.
The invention provides a means to control metal solubility both under regulatory testing such as TCLP testing for hazardous waste classification as well as reducing bioavailability in the open environment without significantly modifying the particulate physical character thus providing for continued use of particulate capture devices such as filters which rely upon free flowing nature of emission fines and non-caking on filters. The preferred method provides for HMP complexing prior to filtration collection in order that the existing facility point source particulate controls remain effective and that compliance with Clean Air Act (CAA) stack emission regulations on total stack particulate emission loading and PM10 loading are complied with. The likely negative impact of adding complexers to the discharge side of the particulate collection devices is that the HMP complexing agent and water could increase measurable total stack emission particulate loading and PM10 loading to levels above allowed and modeled for the specific stack emission, and may also remain less effective than pre-APC application due to the limited time and limited turbulence within the stack flue alone. Another major issue relates to the likely adverse impacts additional particulate and carrying agents of ambient air or water will have on flue gas buoyancy and temperature and possible reductions of stack plume rise. Wet complex agents or slurry agents may be used post-filtration, but similar reduction of flue gas temperature and gas buoyancy as modeled for CAA permitting would likely direct engineers to utilize agent and water injection prior to filtration.
In one embodiment of the invention, the heavy metal bearing particulate from an air emission point source is contacted with a complexing agent and water from the phosphate group in-line prior to exhaust of air emissions from the facility stack. The introduction of phosphates and water into the facility emission stream permits the particulate emissions contact with the introduced PO4 complexing sources and thus converts Pb, Cd, As, Cu, Hg and Zn fine particulates and associated metal oxides and chlorides to phosphate complexed metals which are substantially less soluble and less bioavailable. The introduction of the phosphate complex and water with or without additional complex agents depends on the emission heavy metal compositions and can also be selected by the designer depending on desired contact time and observed complex formation conditions such as temperature, mixing energy and retention variations such as contact time on fabric filters prior to automatic cleaning cycles. The point of complex agent introduction into the air pollution control process will also depend on the particulate size and loading introduced by the complexing agent and the determination as to whether the existing point source particulate and PM10 loading allowances under the CAA will permit complex agent introduction prior to or after particulate control devices. Since most facility stack emissions are closely allowed under CAA permitting and that emission rates are monitored, it is more likely that environmental engineers will elect to introduce complex agents and water prior to APC filtration devices thus not directly increasing particulate loading or reducing exhaust temperatures and entrainment flue buoyancy.
The option to utilize various complexing agents and various points of application provides the environmental engineer flexibility in stabilizing agent recipe selection, with a preferred choice responding to facility stack emission permits, modeling methods and assumptions and the site and use criteria such as TCLP, DI or other biological based toxicity criteria.
The use of water and engineered phosphates such as wet process amber phosphoric acid, wet process green phosphoric acid, aluminum finishing Coproduct blends of phosphoric acid and sulfuric acid, technical grade phosphoric acid, monoammonia phosphate (MAP), diammonium phosphate (DAP), single superphosphate (SSP), triple superphosphate (TSP), hexametaphosphate (HMP), trisodium phosphate, polyphosphates, tetrapotassium phosphate, dicalcium phosphate, tricalcium phosphate, calcium orthophosphates, and combinations thereof would, as an example, provide various amount of phosphate contact with particulates. In certain cases such as use of amber and green acid, such acids embody sulfuric acid, vanadium, iron, aluminum and other complexing agents which could provide for a single-step formation of complex minerals with particulate metals such as lead, cadmium, zinc, copper, arsenic and chromium. The water and phosphate group chemical size, dose rate, contact duration, and application means could be engineered for each type of particulate and process generating the particulate.
As an example, when lead comes into contact with the Pb complexing agent(s) and water, low water soluble compound(s) begin to form, typically a mineral phosphate or precipitate formed through substitution or surface bonding, which is less soluble than the lead originally in the particulate matter. For example, the mineral apatite lead phosphate Ca4(Pb)(PO4)3 OH, lead phosphate Pb3(PO4)2, lead silicate Pb2(SlO3), lead sulfide PbS, chloropyromorphite Pb5(PO)4Cl, corkite and plumbogummite can be formed by adding respective precipitating agents with complexing agents to the particulate. It also remains possible that modifications to temperature and pressure may accelerate of assist formation of lead minerals and complexes, although such methods are not considered optimal for this application given the need to limit cost and provide for optional field based complexing operations that would be complicated by the need for pressure and temperature control devices and vessels. Use of complex agents for mineral formation of lead bearing wastes post-generation is taught by U.S. Pat. No. 5,722,928 issued to Forrester.
Examples of suitable arsenic, mercury, lead, cadmium, chromium, copper and zinc stabilizing agents include, but are not limited to, iodide, hydroxyapatite, activated alumina, activated carbon, bone char, potassium and alumunium salts, ferrioxyhydroxide, potassium permanganate in combination with ferric sulfate or ferric chloride, alum, aluminum sulfate, ferric chloride, ferric sulfate, phosphate fertilizers (e.g., MAP, DAP, SSP, TSP), phosphate rock, pulverized phosphate rock, calcium orthophosphates, monocalcium phosphate, dicalcium phosphate, tricalcium phosphate, trisodium phosphates, phosphate fertilizers, dolomitic limestone, hydrated limestone, calcium oxide (quicklime), calcium carbonates, magnesium oxides, silicates, sodium metasilicates, potassium silicates, natural phosphates and lead mineralizing agents and combinations of the above, phosphoric acids, green phosphoric acid, amber phosphoric acid, black phosphoric acid, merchant grade phosphoric acid, Coproduct solution, hypophosphoric acid, metaphosphoric acid, hexametaphosphate, pyrophosphoric acid, fishbone phosphate, animal bone phosphate, herring meal, bone meal, phosphorites, and combinations thereof. Salts of phosphoric acid can be used and are preferably alkali metal salts such as, but not limited to, trisodium phosphate, dicalcium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trilithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate or mixtures thereof.
The amounts of water and heavy metal complexing agent used, according to the method of invention, depend on various factors including limitations under CAA as well as APC process limitations, particulate character, desired solubility reduction potential, desired complex toxicity, and desired complex formation relating to toxicological and site environmental control objectives. It has been found that an amount of certain complex agents such as activated alumina, bone char, activated carbon, aluminum sulfate, ferric sulfate, ferric chloride, sodium silicate, hydroxyapatite, hexametaphosphate, dicalcium phosphate, tricalcium phosphate, monocalcium phosphate, triple superphosphate, Portland cement, reactive limestone, calcium oxide, diatomaceous earth, pulverized triple superphosphate, wet process amber phosphoric acid, and magnesium oxide, equivalent to between about 0.1% and about 15% by weight of particulate emission is sufficient for TCLP complexing of HMP refuse incinerator flyash, electric arc furnace dust, brass foundry flyash, secondary smelter flyash, shredder dust, utility stormwater fines. However, the foregoing is not intended to preclude yet higher or lower usage of water and complex agent or combinations if needed since it has been demonstrated that amounts greater than 15% complexing agent and 15% water by weight of particulate also work, but are more costly.
The examples below are merely illustrative of this invention and are not intended to limit it thereby in any way.
In this example, municipal solid waste incinerator flyash and scrubber residue fines, collected by baghouse collection devices, ranging from 1.0 to 50.0 micron particulate size containing TCLP and water soluble Pb and Cd were complexed with varying amounts of water and agents including hydroxyapatite (HAP), Dicalcium Phosphate (DCP), Tricalcium Phosphate (TCP), Hexametaphosphate (HMP), activated carbon (AC), amber phosphoric acid (WAA), pulverized triple superphosphate (TSP) and pulverized magnesium oxide powder (MGO). Complexed and un-complexed particulate samples were subsequently tested for TCLP and DI leachable Pb and Cd. Particulates were extracted according to TCLP procedure set forth in Federal Register, Vol. 55, No. 126, pp. 26985-26998 (Jun. 29, 199), which is hereby incorporated by reference, and water extraction by substituting deionized water for the TCLP extraction fluid solution. This test procedure is also referenced in 40 C.F.R. 260 (Appendix 2) and EPA SW 846, 3rd Edition. The retained leachate was digested prior to analysis by ICP.
In this example, electric arc furnace dust fines at 1.0 to 50.0 micron containing soluble Pb, and Zn were complexed with varying amounts of water and agents including amber phosphoric acid (WAA), pulverized triple superphosphate. Complexed and un-complexed particulate samples were subsequently tested for TCLP and DI leachable Pb and Zn. Particulates were extracted according to TCLP procedure set forth in Federal Register, Vol. 55, No. 126, pp. 26985-26998 (Jun. 29, 199), which is hereby incorporated by reference, and water extraction by substituting deionized water for the TCLP extraction fluid solution. This test procedure is also referenced in 40 C.F.R. 260 (Appendix 2) and EPA SW 846, 3rd Edition. The retained leachate was digested prior to analysis by ICP.
In this example, brass foundry flyash fines at 1.0 to 100.0 micron containing soluble Pb were complexed with varying amounts of water and agents including amber phosphoric acid (WAA), pulverized triple superphosphate (TSP) and pulverized magnesium oxide powder (MGO). Complexed and un-complexed particulate samples were subsequently tested for TCLP and DI leachable Pb. Particulates were extracted according to TCLP procedure set forth in Federal Register, Vol. 55, No. 126, pp. 26985-26998 (Jun. 29, 199), which is hereby incorporated by reference, and water extraction by substituting deionized water for the TCLP extraction fluid solution. This test procedure is also referenced in 40 C.F.R. 260 (Appendix 2) and EPA SW 846, 3rd Edition. The retained leachate was digested prior to analysis by ICP.
In this example, smelter flyash fines at 1.0 to 50.0 micron containing soluble As and Pb were complexed with varying amounts of water and agents including Activated Alumina (AA), potassium permanganate and ferric sulfate (KM+FS), ferric sulfate (FS), amber phosphoric acid (WAA), and pulverized triple superphosphate (TSP). Complexed and un-complexed particulate samples were subsequently tested for TCLP and DI leachable Pb. Particulates were extracted according to TCLP procedure set forth in Federal Register, Vol. 55, No. 126, pp. 26985-26998 (Jun. 29, 199), which is hereby incorporated by reference, and water extraction by substituting deionized water for the TCLP extraction fluid solution. This test procedure is also referenced in 40 C.F.R. 260 (Appendix 2) and EPA SW 846, 3 Edition. The retained leachate was digested prior to analysis by ICP.
In this example, wire shredder dust fines at 1.0 to 50.0 micron containing soluble Pb were complexed with varying amounts of water and agents including amber phosphoric acid (WAA), pulverized triple superphosphate (TSP) and pulverized magnesium oxide powder (MGO). Complexed and un-complexed particulate samples were subsequently tested for TCLP and DI leachable Pb. Particulates were extracted according to TCLP procedure set forth in Federal Register, Vol. 55, No. 126, pp. 26985-26998 (Jun. 29, 199), which is hereby incorporated by reference, and water extraction by substituting deionized water for the TCLP extraction fluid solution. This test procedure is also referenced in 40 C.F.R. 260 (Appendix 2) and EPA SW 846, 3rd Edition. The retained leachate was digested prior to analysis by ICP.
The foregoing results readily established the operability of the present process to complex heavy metals particulate thus reducing leachability and thus bioavailability. Given the effectiveness of the complexing agents as presented in the Table 1 thru 6, it is believed that an amount of the stabilizing agents equivalent to less than 1% by weight of particulate emission with water at less than 10% weight particulate should be effective.
While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| 60800960 | May 2006 | US |
