Abstract:
The invention provides methods of remediating lead and other heavy metals in ammunition traps and shooting ranges. One or more remediation agents is added to a trap or a shooting range. The remediation agent(s) interact with and “fix” heavy metals, rendering them substantially non-leachable. An improved ammunition trap is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims priority of U.S. Provisional application No. 60/540,397 filed Jan. 30, 2004, the entire contents of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This application relates generally to remediation of heavy metals, and more particularly to methods for remediating heavy metal ammunition, fragments, fines, and dust found in ammunition traps and on shooting ranges.  
       BACKGROUND OF THE INVENTION  
       [0003]     Lead-Antimony alloys and other heavy metals and their alloys are extensively used for ballistics applications such as bullets and shot. Lead alloy usage is in the region of 200-300,000 tonnes per annum worldwide, of which the USA accounts for approximately half. About 70% of ballistic metals are fired on ranges and it is estimated that there are 9,600 shooting ranges within the USA.  
         [0004]     When bullets or shot are fired on ranges they can, under adverse conditions, give rise to significant pollution through the solublization and corrosion of the lead-antimony alloy in a concentrated area. As shown in  FIG. 1 , pure lead in soft water will yield concentrations of soluble lead levels of above 0.75 mg/litre at pH 7.5 within days to weeks. Lead-antimony alloys will dissolve at a much faster rate and achieve much higher levels of soluble lead, as a result of redox reactions occurring between the lead and antimony metals present in the alloy. ( FIG. 2 .)  
         [0005]     Other heavy metals used for ballistics applications that may be present on shooting ranges include antimony, copper, tungsten, tin, bismuth, silver, nickel, and zinc. All of these metals or their compounds can have a negative impact on human health or the environment.  
         [0006]     To minimize heavy metal pollution, well-managed shooting ranges provide ammunition traps (more commonly referred to as “bullet traps”) behind the target area. Bullets, shot, and other projectiles that are fired pass through the target and impact a bullet stop or “trap,” and their impact fragments are contained. Periodically, the traps must be refurbished and the spent bullet fragments removed for recycling.  
         [0007]     There are many different designs of bullet traps. A partial list includes plate and pit, escalator, venetian blind, rubber lamella, granular rubber, and circulating water (snail trap). In general, most bullet traps fall into two main categories:  
         [0008]     Type A: Boxes or similar devices containing materials to absorb the mechanical impact of the projectile, e.g., sand, rubber, hydro-gel blocks, rubber or polyurethane curtains, and similar materials.  
         [0009]     Type B: Large steel plates to direct projectiles toward a moving liquid energy dissipation system. Such systems usually utilize flowing water, oil, or similar liquid to minimize abrasion and impact damage within the trap.  
         [0010]     Combinations of the two types are also sometimes employed. Hence, a trap may contain both an ammunition impact-absorbing and/or deflecting means (e.g., impact plates, deceleration chamber, sand pit, moving fluid, rubber strips or curtains, etc.), and a receptacle for collecting bullet fragments, fines, and/or dust. While minimizing dust, conventional bullet traps still give rise to fines and other fragments which, on exposure to the environment, can corrode to yield soluble lead salts that may be transported to the drainage system of the range by action of rainwater. Additionally, liquids used in traps of Type B can give rise to heavy metals-contaminated wastes resulting from the corrosion of lead dust and fines in the circulating lubricant systems. What is needed are improved, environmentally self-remediating ammunition traps, and methods for rendering an existing trap self-remediating.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention addresses the problem posed by heavy metal-based ammunition in ammunition traps and shooting ranges, including contamination from spent ammunition, ammunition fragments, fines, and dust. According to a first aspect of the invention, a method of remediating a heavy metal in an ammunition trap is provided, and comprises adding to the trap at least one heavy metal remediation agent. As used herein, the term “heavy metal remediation agent” (or more simply, “remediation agent”) refers to a substance that is capable, either alone or in combination with one or more additional substances, of “fixing” a heavy metal, either by transforming it to a less water-soluble form and/or by otherwise rendering the heavy metal substantially non-leachable (i.e., by encapsulating the metal in a substantially non-leachable matrix). Preferably, the remediation agent is capable of reducing the water-solubility of a heavy metal below the maximum amount permitted by statute, e.g., the U.S.-U.T.S. limits. For lead-based ammunition, a combination of calcium sulfide, calcium carbonate, and calcium phosphate (or triple super phosphate) is preferred. In one embodiment, one or more remediation agents is added to an ammunition trap as a block or pellet, a flake, a free-flowing powder, a slurry, or some other suitable form. In the presence of water, the remediation agent interacts with heavy metals from spent ammunition, bullet fragments, fines, and/or dust, and remediates the heavy metal(s) in the trap.  
         [0012]     According to a second aspect of the invention, a heavy metal remediation block or pellet for use in a bullet trap and/or shooting range, and a method of making same, are provided. In one embodiment, a remediation block or pellet comprises at least one remediation agent dispersed or otherwise contained in a water-soluble or water-degradable binder or matrix. Optionally, the block or pellet further comprises one or more surfactants, dispersing aids, and/or flocculating agents to assist deposition of precipitated insoluble metal compounds. Such a block can be formed, for example, by forming a mixture of at least one remediation agent and a water-soluble or water-degradable binder; creating a melt by heating the mixture; and forming a pellet or block from the melt. Remediation block formation can be based, to a degree on the principles of Integrated Fixation Systems technology detailed by Webster and Hurley in U.S. Pat. No. 6,838,504, the entire contents of which are incorporated by reference herein.  
         [0013]     According to a third aspect of the invention, a method of remediating a shooting range contaminated with at least one heavy metal is provided, and comprises: introducing one or more remediation agents into a drainage system of the shooting range, or, particularly in the case of an outdoor shooting range, allowing one or more remediation agents to contact the shooting range (i.e., the ground). Adding a remediation agent or agents to a shooting range&#39;s sump, pond, drainage line, etc., or simply the ground itself, enables the agent(s) to interact with heavy metals from spent ammunition, ammunition fragments, fines, or dust, thereby preventing soluble lead, antimony, and other heavy metals from being discharged into public water courses.  
         [0014]     According to a fourth aspect of the invention, an improved ammunition trap is provided and comprises at least one heavy metal remediation agent in combination with an ammunition trap. In one embodiment, an improved trap comprises at least one ammunition impact-absorbing and/or deflection means; a receptacle for spent ammunition, fragments, fines, and/or dust; and at least one remediation agent in the receptacle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The advantages and various features of the invention will become better understood when reference is made to the following detailed description and considered in light of the accompanying drawings, wherein:  
         [0016]      FIG. 1 . is a graph showing the corrosion of a 2 mm shot of 99.999% lead immersed in water for 100 days;  
         [0017]      FIG. 2 . is a graph showing the corrosion of a U.S. No. 8 lead-antimony shot (nominally sold as containing 2% antimony, but actually assayed at 1.25% antimony (w/w); and  
         [0018]      FIG. 3  is a schematic illustration of one embodiment of a self-remediating ammunition trap according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     According to one aspect of the invention, a method of remediating one or more heavy metals in an ammunition trap is provided. In one embodiment, the method comprises adding to the trap at least one remediation agent. Nonlimiting examples of remediation agents include calcium sulfide, calcium phosphate, calcium hydroxide, calcium oxide, calcium carbonate, magnesium sulfide, magnesium phosphate, magnesium hydroxide, magnesium oxide, magnesium carbonate, apatite, di-calcium hydrogen phosphate, calcium di-hydrogen phosphate, triple super phosphate, dolomite, phosphoric acid, and/or mixed calcium adducts of these agents. Other examples of remediation agents include phosphoric acid and its salts, which can be used for lead abatement; the mineral apatite (Ca 5 (PO 4 ) 3 (F,Cl,OH), which is functional, but slow; alkaline earth silicates (e.g., calcium silicate), which operate through sorption and as a consequence of their high alkalinity (hence, their effect is likely not permanent); hydrated silica and hydrated alumina; and metal-sorbing clays, such as Bentonite and Fuller&#39;s Earth. When used by themselves, phosphates are considered suitable for remediation of lead, but they do not remediate other metals.  
         [0020]     Environmental remediation agents are available from Solucorp Industries (West Nyack, N.Y.) under the Molecular Bonding System™ or MBS™ trademark, and Metals Treatment Technologies (Wheat Ridge, Colo.) under the Ecobond® trademark. Preferred remediation agents comprise mixtures of technical grade calcium sulfide, calcium phosphate or triple super phosphate, and calcium carbonate, available from Solucorp Industries. “Triple super phosphate” (also referred to as tri-super phosphate, or TSP) is Ca(H 2 PO 4 ) 2 .H 2 O (CAS No. 65996-95-4). A particularly preferred remediation agent for lead and lead-antimony alloy ammunition is MBS™ 2.1, a 3:2:1 (wt/wt) mixture of calcium carbonate, calcium sulfide, and triple super phosphate. MBS™ 2.1 is not pH-dependent, and can remediate lead under conditions ranging from pH 1 to pH 13. In contrast, phosphates and silicates are pH-dependent, with phosphates functional under broadly neutral conditions (pH 6 to 8), and silicates functional under strongly alkaline conditions (&gt;pH 10). Additionally, the MBS™ remediation agent converts soluble lead salts to lead sulfide, which is non-toxic by oral administration.  
         [0021]     The remediation agent(s) is added to the trap as a remediation block or pellet, flakes, a free-flowing powder, a slurry (e.g., an aqueous slurry of one or more remediation agents), or in some other suitable form. Remediation blocks are particularly preferred, as they permit the remediation agent(s) therein to be released in a time-release fashion, with minimal increase in the alkalinity of the system. Applying the remediation agent(s) at too fast a rate, in addition to being wasteful, may lead to a temporary increase in dissolution of fine lead metal fragements in the sludge of the trap, requiring a longer time for the reagent to be fully effective.  
         [0022]     The amount of remediation agent(s) added to the trap depends on the type of trap, the type and amount of heavy metal contamination, the particular remediation agent(s) employed, and other factors that will be appreciated by a skilled person. Traps that see substantial use in a given period of time will typically require larger amounts of remediation agents than traps that see little or infrequent use.  
         [0023]     Whether in block, pellet, flake, powder, slurry, or some other form, the remediation agent is added to a region or regions of an ammunition trap most likely to be exposed to spent ammunition, ammunition fragments, fines, or dust; for example, the pit in a pit-and-plate trap; the sump, water line, or liquid tank in a circulating fluid trap; a receptacle near a deceleration chamber or impact-absorbing plate; or any part(s) of the trap likely to be exposed to heavy metals.  
         [0024]     For example, in one embodiment, one or more reagent blocks are placed in a type A ammunition trap (described above) where lead fines may occur. On exposure to moisture, which may cause the onset of the corrosion of the lead fragments collected by the trap, the block(s) are activated and liberate their remediation agent, causing continual remediation of the spent lead fragments within the trap during its active use. The block(s) may be replaced during periodic maintenance of the trap. Alternatively, the reagent blocks are incorporated into a rubber-like hydro-gel or other materials from which bullet trap energy-absorbing materials are constructed.  
         [0025]     In another embodiment, one or more reagent blocks are applied directly to a type-B trap (described above) and will disperse in the liquid systems to remediate lead fines and corrosion products. Spent lead that is removed for recycling, though it will be darkly coloured with a passivating corrosion product, and rendered stable to further oxidation and corrosion, will still be recyclable in the same manner as untreated lead. Addition of the reagent blocks to the liquid lubricants will render the lubricants free of soluble lead and reduce the risk of a liquid waste hazard, with a consequent reduction of waste disposal costs.  
         [0026]     In a second aspect of the invention, a heavy metal remediation block or pellet, and a method of making such a block or pellet, are provided. In one embodiment, a heavy metal remediation block or pellet comprises at least one remediation agent dispersed or otherwise contained in a water-soluble or water-degradable binder or matrix, the composition being of a suitable size and shape (small or medium block, pellet, etc.) to function within one or more areas of the trap. When exposed to water, the binder dissolves or degrades over a period of time, releasing the remediation agent, which interacts with and fixes lead, antimony, and other heavy metals in the trap.  
         [0027]     Nonlimiting examples of binders include water-soluble and/or water-degradable waxes, such as hydratable and/or degradable polyethylene glycols and copolymers of ethylene glycol; polyacrylates and/or hydratable celluloses compounds, and their methyl, ethyl, propyl and/or butyl ethers. Mixtures of binders may also be used.  
         [0028]     Optionally, the reagent block or pellet further comprises one or more surfactants, dispersing aids, and/or flocculating agents. Nonlimiting examples of useful surfactants and dispersants include polyethoxyethylene ethers of fatty acids, polyethoxyethylene esters of fatty acids, and polyethoxy ethers of alcohols (e.g., polyether alcohols having the formula CH 3 (CH 2 ) x —O—(CH 2 CH 2 ) y —OH, where x &gt; or =5 and y&gt;1). Typical surfactant concentrations within a reagent block are 0.1 to 1% by weight of the total block. Nonlimiting examples of flocculants include Superfloc A120, A130, and A150, from Cytec Industries B.V.).  
         [0029]     A heavy metal remediation block or pellet can be formed in a straightforward manner. In one embodiment, the method comprises forming a mixture of at least one remediation agent and a water-soluble or water-degradable binder (and, optionally, one or more surfactants, dispersing aids, and/or flocculating agents); creating a melt by heating the mixture; and forming a pellet or block from the melt. For example, a block or pellet can be “cast” by pouring the melt into a mold and allowing it to harden. Pellets or blocks so formed can added to an ammunition trap to remediate heavy metal ammunition fragments, fines, and dust.  
         [0030]     To increase production speeds, the remediation blocks and pellets may be formed by a number of mass manufacturing processes, e.g. prilling or compressing into blocks or tablets; flaking; etc., and the invention is not limited by the physical methods of preparation of the blocks described herein.  
         [0031]     In another aspect of the invention, heavy metals from spent ammunition, ammunition fragments, dust, fines, etc. on a shooting range are remediated by introducing one or more remediation agents into the drainage system of an indoor or outdoor shooting range (e.g., a sump, pond, and/or drainage line), or simply the ground itself in an outdoor range. The remediation agent(s) interact with heavy metals from spent ammunition, ammunition fragments, fines, dust, etc., thereby preventing soluble lead, antimony, and other heavy metals from being discharged into public water courses.  
         [0032]     According to a fourth aspect of the invention, an improved ammunition trap is provided and comprises at least one heavy metal remediation agent in combination with an ammunition trap. In effect, the trap is “environmentally self-remediating,” as it remediates lead and other heavy metals from ammunition that enters the trap. In one embodiment, an improved trap comprises at least one ammunition impact-absorbing and/or deflection means; a receptacle for spent ammunition, fragments, fines, and/or dust; and at least one remediation agent in the receptacle. In alternate embodiments, the trap has an alternate configuration and/or the remediation agent(s) is disposed elsewhere within the trap.  
         [0033]     Referring to  FIG. 3 , an improved ammunition trap in accordance with one embodiment of the invention is shown. The trap  10  is of the circulating water type (sometimes referred to as a “Snail Trap”), and includes a deceleration chamber  12  through which water circulates. A bullet or bullet fragment  14  enters the trap and travels along a path  14   a  until it contacts the deceleration chamber and stream of circulating water. The bullets travels around the chamber until it loses its kinetic energy and falls through a gap  16  in the chamber and is caught by a screen or grill  18 . Smaller bullet fragments, fines, and dust, as well as water, pass through the screen  18 , and are retained in a receptacle  20 . The receptacle also acts as a reservoir for water used in the system. Over time, sludge accumulates at the bottom of the reservoir. Water from the receptacle is pumped through a return line  24  back to the deceleration chamber  12 .  
         [0034]     According to the invention, one or more remediation agents  30  is introduced to the trap, either as a block, pellet, powder, slurry, or other form, by adding the same to the water reservoir/receptacle  20 , an input line (not shown), or some other suitable location. If a block or pellet of the type above is used, it has the advantage of releasing remediation agent(s) into the system at a measured rate; that is, in a time-released fashion.  
         [0035]     The following are nonlimiting examples of the invention:  
       EXAMPLE 1  
       [0036]     A heavy metal remediation block consisting of technical grade calcium sulphide, calcium phosphate, calcium carbonate, polyethylene glycol wax (approx. mol. weight 1,500) in a wt.-to-wt. ratio of 2:1:3:2) is prepared by blending the ingredients together, heating the blend to 100° C. (thereby causing the wax to melt), and casting the melt into 5 gram to 100 gram blocks. A reagent block approx 0.5 inch square will disperse in water in 24-48 hours.  
       EXAMPLE 2  
       [0037]     A heavy metal remediation block consisting of technical grade calcium sulphide, calcium phosphate, calcium carbonate, calcium hydroxide, polyethylene glycol wax (approx. mol. weight 1,500) in a wt. to-wt. ratio of 2:1:1:2:2 is prepared by blending the ingredients together, heating the blend to 100° C. (thereby causing the wax to melt), and casting the melt into 5 gram to 100 gram blocks. A reagent block approx 0.5 inch square will disperse in water in 7-14 days.  
         [0038]     A 5 g block prepared as described herein, when dispersed in water, will adsorb in excess of 1.8 grams of soluble lead. If an excess of reagent is used (relative to the amount of soluble lead present) leachate levels are reduced below UTS limits by US-TCLP testing procedures.  
         [0039]     Immersion of a 5 g block prepared according to example 2 in water for a period of 21 days resulted in no discernible decrease in chemical efficacy. Immersion of the same size blocks in running fresh water for 21 days, followed by exposure to soluble lead, resulted in only a 10% loss of efficacy. Dissolution and or longevity of the efficacy of the treatment block may be controlled by block size and shape.  
       EXAMPLE 3  
       [0040]     A heavy metal remediation trial was conducted on four circulating-water bullet traps (also known as “Snail Traps”), supplied by Savage Range Systems (Springfield, Mass.) in an indoor shooting range. Several thousand rounds of ammunition are fired on the range annually. Four, 8-foot wide bullet traps were situated in a row immediately behind a 30-foot wide target area. The sumps of the traps were interconnected to make one combined sump operation below the deceleration chambers of the four traps. Bullets passing through the targets pass into the traps and are carried on the traps&#39; circulating-water systems until they loose their ballistic energy and are deposited on a bullet capture screen below each trap. Owing to the construction of lead-antimony alloy and other frangible bullets, a small proportion of each spent slug may be carried by the circulating-water system and subsequently settle as a sludge (in this case equating to approximately 72 cubic feet) in the water sump or reservoirs situated immediately beneath the traps. Combined, the four traps contained approximately 280.5 gallons of water containing 1% of a conventional alcohol glycol-based antifreeze. Prior to treatment, the water circulating in the traps (being a composite of the sludge and water) exhibited 173 mg/liter of soluble lead. The sludge exhibited 1,340 mg/liter of soluble lead (by TCLP SW846 procedure)  
         [0041]     20 lbs of a remediation agent (MBS 2.1, from Solucorp Industries) was added to each of the four traps, equating to a treatment dosage of 3.44%, and the traps maintained in active range use for a further six weeks. Post-treatment and curing, the soluble lead in the water circulating in the traps had fallen to 7.68 mg/liter, and the sludge exhibited 2.87 mg/liter of soluble lead (by TCLP SW846 procedure).  
         [0042]     The invention has been described with reference to various embodiments, figures, and examples, but is not limited thereto. Persons having ordinary skill in the art will appreciate that the invention can be modified without departing from the invention, which is limited only by the appended claims.