^■ CROSS-REFERENCE TO ELATED APPLICATION

(0001 ] This appiicatiofi claims the benefit of U.S. provisional patent application no. 62/562.257, fifed ^' September 22, 2617, the entire contents of which are incorporated herei by this reference.

FI LD OF THE INVENTION

[0002] The .invention relates to methods for reraediattng mercnry-contaminaied soil and waste, BACKGROU D ^' OF THE INVENTION

[0003] With the expanding world-wide f®guiatory ba on the use, import, and export of mercury and its ^■ ■compounds—onic as well as eovalent-— and waste materials that contain .mercury, there exists a substantial need for a simple but effective method for converting mercury found in soil sediments, ore residues, and other mercury concentrates, solid wastes, debris, etc. to chemically stable forms suitable for long-term disposal, in recent years, many management approaches to mercury and mercury-bearing materials have focused on recovery and recycling of mercury in its elemental form, using retort and other thermal means. Unfortunately, these recovery options are not viable for many situations, both from the perspectives of cost and. efficacy, and toxicity to humans and the environment, Although regulation s governing th e reuse of elemental mercury have become increasingly stringent and manufacturers have .shifted to other more

environmentally sound, less toxic options, numerous contaminated sites remain untreated, hi addition, new sources of mercury contamination are likel to he identified that require remedial cleanup. Accordingly, ^' there remains a need for safe and effective methods for addressing the management and di sposal of historic mercury contamination .found in. soil, solids, and other materials, and new contaminated sites as they are identified in the sear future. This invention converts mercury in its elemental and other forms into a chemically stable state of reduced, solubility and ieaehability for safe, .low-cost disposal via internment

[0004] Over the years, much, attention has been paid to the treatment of mercury in soil, solid waste, and other materials. These technologies have relied upon recovery of mercury usin retort or other thermal processes, or various chemical techniques. Examples include mixing the contaminated material with sulfur and caickra-feased sulfides, controlling pH using calcium (and/or magnesium) alkaline earth agents, and. introducing ealer n^based-phosp at and phosphate sail additives to mitigate iron, issues. Other techniques for remediating mercury contaminants include the use of less effective polysnlf de, other heavy meia!s to hel complex formation, and oxidation/reduction reaction, drivers to -convert mercury to more or less reactive forms for scavenging or other recovery or capture methods..

[0005] While prior approaches to mercury remediation may be effective in. some situations, they have a number of drawbacks. For example, thermal methods generate elemental mercury with severe reuse/disposal options and significant energ requirements. Some .chemical, techniques expand - the -end-product treated- mass and volume by the incorporation ©fhydrated water and the amounts of solid reagent and water added. Some techniques utilize absorbents, adsorbents, phosphate-bonded ceramics, or other specific: resins to physically retain, soluble mercury within the addi tive matrix or media component, and as- such are quite complex.. And some of the chemical techniques require the addition of three or more reagents to control: mercury solubility; interferences from various species (e.g., iron) found in the waste, material .or soil; and pH in the neutral to alkaline range, using linie, calci m -based hydroxides or carbonates.,

[0006] The mercury remediation method of the present invention forms mercury sulfides and metallic phosphates of educed solubility and teachability with the addition of calcium sulfide and TriscxK n phosphate (TN&F). When TNaP enters solution with water, sodium ions _, are released that do not react with sulfide to -compete- with mercury sulfide reactions, unlike the calcium provided by calcium-based phosphate reagents. TNaP also forms hydroxide in tbe- presence ©f water, which facilitates overall reaction pH in the alkalin range to prevent loss of sulfide as hydrogen sulfide. This avoids a substantial health risk (j¾S- is toxic), and ensures that an appropriate quantity of sulfide is available to react with mercury to form virtually insoluble mercury sulfide. Also of importance, the invention' s reagents do not cause water hydration of the treatment reactants or end-pnoduct mass. Hydration reactions with cement and other pozzolans not only detrimentally incorporate-water mass into the treated end-product, hat ^' they generate heat, and mercury is easily volatilized from solid and water materials to extremely toxic vapor forms at even slightly elevated temperatures. [0007] The Patent literature describes a number of approaches for remediating mercury.. US 4,14?.6 ^" 26 addresses the Treatment of Mercury Contaminated Aqueous Media where calcium. polysBlrl.de is. used to. react with elemental mercury to form mercury sulfide. US ,5,034,0.54 speciflesvs EProcess .fo Treating Mercury in Preparation tor Disposal by treating elemental mercury using metallic powders such as copper, nickel, zinc, or sulfur to form, a solidified mass where mercury is absorbed to the elemental surfaces of the added metals. ITS 5,226,545 calls for the Extraction of Mercury and Mercury Compounds from Contaminated Material and Solutions and removal of mercury from host matrix using an oxidant and iodine based additives- US 5,314,527 treats Mercury Contaminated Mod using a hydronietaliurgical method that includes providing: an acid and sodium hypochlorite through a series of treatment processing steps- and thickening the material to extract mercury from US EPA listed l 06 waste derived from mercury chlor-aikali plants. US 5,397,478 relates to the fixation and stabilization of chromium in contaminated materials. US 5,536,89 teaches the use of a complexing agent of aluminum or iron, chloride, and preferabl phosphoric acid, or a variet of other water soluble phosphoric acid salts containing phosphates for the treatment of lead, where one type of phosphate salt is Trisodiurn phosphate,. Howe ver, the inclusion of ealcinm sulfide i s not taught, no -is the treatment of elemental, or other mercury forms.US 5,877,393 describes a Treatment Process for Contaminated Waste containing metals thai teaches the necessary use of three (3) reagents that inciude calcium sulfide, an inorganic phosphate selected from various calcium phosphate forms, and calcium hydroxide, calcium carbonate, or caieiura oxide and or mixtures: of calcium-based -pH control components to render toxic metals harmless.. The invention uses calcium, phosphate to prevent remobilization of the contaminating metal such as iron and othe metals with various o¾idation-red action vaienee.US 5,898,093 is a Treatment Process for Contaminated Waste: that teaches the use of three (3) reagents including calcium sulfide: or calcium, poly sulfide, calcium phosphate, and calcium carbonate to treat teachable toxic heavy metals, and in particular, lead in solids and soli. Calcium phosphate is provided to react with ferric iron to prevent a redox potential that will oxidize metallic sulfide. The preferred calcium phosphate is calcium hydrogen phosphate. To supplement basic pH requirements, calcium oxide is ^• recommended. US

6,258,018 causes Fixation, and Stabilization of Metals in contaminated soils and materials using phosphoric acid and sulfate and does not: esolve mercury treatment or prescribe sulfide use. US 6,309,337 Is a method like '018 for forming an insoluble phosphate mineral species using phosphoric acid and sulfate and. does not teach mercury treatment or sulfide use. US 6,475,451 addresses Mercury Removal from Gaseous Process Streams using an oxidizer such as nitric acid to scavenge mercur for gaseous process streams. US 6,635,796, like ' ^' 0,18 ^· and L337, provides a method for the reductioa of leacfeahiiity and solubility of radionuclides and radioacti ve substances in .contaminated soils and materials using phosphoric acid and sulfate and does not teach, treatment of mercury or sulfide use, US 6,838,504 Bl is an Integrated Fixation Systems that teaches the use multiple reaetants of polymeric matrices and films- comprised of sulfides, phosphates and adsorbents to reduce teachability of heavy metals to produce; insoluble metal compounds, and ^' in particular _* , for the. use in the ^' m nufa ture, of lead-acid batteries. US ^'

6,9 1,570 provides for a Method for Fixating Sludges and Soils Contaminated with Mercury and oilier Heav Metals tha-t ^' ieaches .the use of a sui&r-cootaining -compound such -as sulfide, po!ysulfide. thiolcarbamates or mixtures, ^· hereof, and. the additio of i ron-compounds and oxygen with agitation or sparging. US 7,208,457 B2 is a Heavy Metahl¾mediatmg Paint Strippe that uses more than two (2) reagents including; eaieiurn sulfide, calcium carbonate, and triple superphosphate mixed with soybean, oil and N-metbyl pyrrolidone to render heavy metals, primarily lead, insoluble when appl ed to heavy metal-based paint for its removal by the stripping In vention, US 7,407,602 provides a method for controlling air pollution for mercury and other pollutants where a eomlmsiion gas is passed through a slurry of an alkaline-earth metal sulfide and -a redox buffering agent such as phosphate, and preferably with an alkaline-earth carbonate and/or hydroxide. The Invention removes heav metal from combustion gas where the composition of the slurry is provided as an aerosolized aqueous dispersion in a 20-50% (w/ ). solids dispersion mat can be applied to the combustion gas using a spray no zle or rotary atomizer-. US 7-670.576 describes Methods of Treatment, of Chromite Ore Processing Residue containing hexavaient chromium and teaches the use of providing oxygen scavengers and a ehemical reducer to treat chromium using ferrous iron/ferrous sulfide, US 7,771,683 expands: on the '602 patent' s di sclosure b specifying the use of calcium and/or magnesium, based aikaiine- earth metal sulfides, hydroxides, carbonates, and phosphates.

[0008] Other ^' Published irt-Related Literature inckd.es Ahmad, ZaM, "Principles of Corrosion Engineering and Corrosion Control ' Chapter 11 - Boiler Corrosion, pp .576-608, Elsevier Ltd,, 2006; Conner, Jesse FL, "Chemical Fixation and Solidification of Hazardous Wastes", ¥an Nostrand Reinhold, NY,NY(1990); Clever, H . _S Johnson, S. A.., and Derrick,- M.E.. "The Solubility of Mercury i Some Sparingly Soluble Mercury Salts n Water and Aqueous

Electrolyte Solutions," X Phys.Cheni.. Re . Data, 14(3), 631-680, 1985; Bagermann,

"Technologies for the Stabilization of Elemental Mercury and Mercury-Containing Wastes," Gesellsehafi for Anlagen-rund Reaktorsieherheit mbE. October .2009; Ralb. Adams, MiHan, "Sulfur Polymer Siabilizaiion/Solidifkation (SPSS) Treatment of Mixed-Waste Mercury

Recovered from EftVironmfental Restoration Activities at BNL, Brookhaven National

Laburatory,. EuvirorsBienia! Sciences Department, USD0E.. January 2001; Piao, Haisban, "Stabilization ofMercury-containing Wastes Using Sulfide," Ph.D. dissertation submitted to the: Division of Research and Advanced Studies of ^' the Universit of Cincinnati, Departmen of Ci vil and Environmental Engineering of the Gollege of Engineering, 2003; Rodriquez:, Padilla, Tayibi, and Lopez-Dekgado, "Concerns on Liquid Mercury and Mercury-Containing Wastes: A Review of the Treatment Technologies the Safe Storage (of mercury). National Centre of Metallurgical Research, CEMIM, CISC Madrid, Spam; Yost, Pal, CMsicL and. Jeserrrig, "Lead and Other Heavy Metal Fixation in Soils and Solid Waste by the MAEiCTlTE® Chemical ^' Ireatment Process", 49 ^fe Annual Purdue Industrial Waste Conference, May 1994; U.S. EPA Capsule Report, "Aqueous Mercury Treatment," Office of Research and Development, Washington., DC, EPA 625.R-97/O04, My 1997; and Yost, Chisiek, and Mueller, "Reduction of Radionuclide and Other Radioactive S«bstattce _: teachability from: Ohio and Mew Jersey Soi.fs _: Using an Innovative Chemical Treatment Process*'. 51 ^st Annual Purdue industrial Waste Conference. May 1 96.

[0009] Notwithstanding the prior attempts to address mercury contamination in industr and the environment, there remains a need for safe and effective methods for treating ^' historic mercury contamination found in soil, solids, nd other materials, to- safely dispose of recovered mercury, and to handle new contaminations as they occur or are identified in the near future.

SUMMARY OF THE INVENTION

[00 i 0] The present invention provides a method for treating leachable elemental mercur and other mercury species in solids, soils, and other wastes using calcium sulfide (CaS) and Tri- sodiure phosphate (TNaP; Ν%Ρ£> ₄ ) in order to convert m mercury o less leachable forms and to bring the contaminated material into compliance- with various statutes and regulations, including The Resource Conservation Recovery Act (42 IJ.S.C. § 6901. -et seq A Title 42 of the Code of Federal ^' Regulations, and related United States &nvifomiientai Protection Agency (U.S. EM) directives and guidelines relating to land disposal an waste management.

[0011] This invention converts- mercury in its elemental and other forms ^' to a chemically stable state of reduced solubility and leachabilky suitable for safe, low-cost disposal via internment n particular, elemental, ionic, and organic mercury forms are preferentially and chemicall converted by the invention reagents to highly ^' insoluble forms stable to EPA test methods, ineludiii Method 1311 Tox city Characteristic Leaching Procedure— TCLF - Revision 0, 1992) and Method 1312.( ynthetic Precipitation Leaching Procedure; -- SPLP) for acid rain exposure. Unlike common physical binding technologies where mercury is solidified i a.

stabilized physical mass using cements, pozzolans, or -other such geoteehnieal- -based

immobilization a roaches; the present Invention utilizes chemical bonding principles to generate mixed- mineral forms that are resistant to leaching .from H, landfill leachate constituents, and abrasive mechanisms associated, with particle-to-particle eontaci encountered in waste handling, landfill mtemment compaction, cover placements, and in situ ^e a^i n " within the landfill Physical mass dimension .stability of material treated by this i vention is not essential to the long-term chemical stability of the mercury forms in treated materials.

[001.2] According to one. aspect of the invention, a method of treating mercury^co-ntarninated material to obtain a remediated product having reduced mercury teachability includes the steps of (a) admixing the ffiercin-y-eontaruinated material with a reagent system comprising calcium sulfide (CaS)-and trisodi m phosphate (TbaP), wherein the calcium sulfide and triscdiurn phosphate are provided at a Ca.S:TNaP ratio of from 2: 1 to 1 :2, on a dry weight reagent basis, and the reagent system is provided in an amount equal to 0.4% to 5% by weight of the contaminated material; and (b) adding water as needed to achieve a moisture content of at leas 5% by weight of the contaminated material. The mercury-contaminated material can be provided as a dr solid, a moist solid having a moisture .content of up to 60% by weight (for example, contaminated soil), a sediment, sludge, or slurry having a solids content of at least 5% by weight, or the material may have some -other physical form or an aggregation of . forms.

[0013] The addition of eaieiurn sulfide (CaS) and trisodiom phosphate |W , NasPO*) ^' to mercury-containing materi al ill preferential ly cause mercury to form precipitates of mercury sulfide of reduced solubility and teachability within the host solid matrix. The binary reagent system described herein has several ad antages over the prior art, including ease of use, pH control, limited mass Increase, reduced cost, the ability to optimize reagent dosing to treat soils and waste having varying degrees of mercury contamination, and most significantly the ability to meet the requirements for handling hazardous waste under the U.S. EPA RC A Toxicity Rule for characteristically hazardous waste.

DETAILED DESCRIPTION

[001 ] As provided by one aspect of the invention, the addition of calcium sulfide (CaS) and trisodinm. Phosphate ("TNaP Na^PC^) to rEierctiry-contairiing material will preferentially cause mercury to form precipitates of mercury sulfide of reduced solubility and teachability within, the host solid matrix. Mercury teachability is measured using the US. EPA' s SW-846 Test Methods for the Evaluation of Solid Waste, where solid materials are prepared .using _. Test Method 1311 (TCLB - Toxicity Characteristic Leaching Procedure - Revision 0, 1992), and the resultant extract fluid is analyzed for total mercury. Under the U.S. EPA RCRA Toxicity Rule- for characteristicall hazardous waste, mercury concentrations m the extract greater than.0.2 mg/L classify the material as a characteristically hazardous waste. Mercury in TCLP extract, at concentration of greater than 0,025 mg L tails to meet the .U.S. EPA's Uni versal Treatment Standard for mercury in characteristically hazardous waste,

[00:15 j Each reagent -is equall important to the reaction process. In general and without showing the speeiaiion of mercury, the raercury-sulfide reactions of the technology stated simply are given in equations (1) and (2);

(1) GaS + ! !;;() -→ CatStf)(OH)

(2) ea(SH}(0:B) ÷ Hg -f H ₂ 0 -→ CaiC)H? ₂ + HgS.| .

[0016] The general disassociation reactions for T aP in w ter include those shown in equations (3) and (4):

(3) Na ₃ PQ ₄ (s) -→ 3Na ⁺ (aq) + PO/ aq) (4) Na ₃ P0 (s) + H ₂ 0→ NaOH(aq) + Ma ₂ .Hi?0 „ where calcium sulfide is a partially water sol able, solid reagent powder that supplies -St le sulfide ions to the process; aad where, trisodium phosphate- (TMaP) a highly water, soluble solid that provides look- phosphate and alkaline pH conditions when dissolved in water. When CaS and TNaP are properly combined and the reagents are admixed with a mercury-containing material (with, water added as needed to rai se the moisture content of the contaminated M eri l to at least 5% by weight), the desired highly insoluble, nonTeacliab!e and stable mercury sulfide is preferentially formed.

[0017] The CaS and TMaP reagents can be added to the contaminated material in combination, or individually., with CaS added separately from TMaP, The reagents-: can be pro vided in dry form or, alternatively, either or both of the components of me reagents can be provided as an aqueous slurry , if the reagents are -added, as a slurry (or . as individual slurries), the water contained therein can be sufficient to raise: the moisture. content of the .contaminated material to the desired -minimum of at least 5% water by weight.

10018] Calcium has an. affinity for sulfide, and CaS has a- tendency to. remain -as partially insoluble solid a provided I its reagent xbmu As shown in Table 1 below, the solubility product constant ( _s¾> ) for CaS in water is 8.0 xl-0 ^"6 ax 25 ⁹ C. Calcium provided by the GaS reagent will tend to remain in its stale bound to sulfide, thus reducing the availability of sulfide to react wit mercury. (Similarly, any calcium, present in the host waste material will tend, to react with sulfide, further dlmmis ng the availability of sulfide to react with mercury.) The present invention addresses this problem b including TNaP as a ..component of the reagent system.

(0019] When dissociated in water, TNaP provides reactive phosphate ions to form highl insoluble calcium phosphate, as shown in equation 5:

(5). Ca ^{" "-} + r > Ca¾(POi)2l -

B [0020] Calcium phosphate has a -Κ _ψ of 2,07* 10 ^" "" at 2S°C, Phosphate iocs released when the T aP reagent is dissolved in water react preferential ly with caiciora. This effectively removes calcium from competing with mercury for sulfide, and allows free sulfide released from the CaS reagent to react preferexnially with, the mercury. Tabic 1 presents common . solubility product constants that are widely published in the literature. 0021]

Reagents, Ead-pr >d¾e s, ¾¾d _. Fr gj^^ggP _. ^

Compound sp 25°C Comment

Mercury (h) sulfide 6.44x10 ^{¾ <} invention end product

Mercu y {1} sulfide 1,0.x 1 ^Q * ^? invention end product

Calcium phosphate 2.07X10 ^'33 invention end product/not added as invention reagent {or In similar salt fern s)

Mercury {iij hydroxide 3.60 l0 ^'¾ invention end product/unstable in presence of sulfide

ercury (!) hydroxide 3.13x10 ^" invention end product/unstable in presence of sulfide

15

Mercury (!) carbonate. 9.52. x 10 Carbonate not provided in present Inven tion

Calcium carbonate 4,·96 ^χ .10 ^"9 Carbonate not provided in present Invention

Calcium hydroxide 4.68X10 ^'6 Not -p esided as invention reagent/unstable in presence of phosphate in controlled alkaline condition

Calcium sulfide Preferred invention reagent - not stable in presence of phosphate Tmedsyrn hos hate Preferred invention reagent - highly water soluble

Calcium pofysuifjde Invention reagent - highly water soluble/excessively elevates p-H when

additionaf suifide is required

Mercury (!) phosphate unknown NC/NR

Mercury (i!) phosphate unknown HC/m

Mercury (H) carbonate unknown n /m

[0022] It is well known that the lower the sp value of a compound, the lower the solubility o that compound in water at the reported temperature. Of course, published Ksp val ues are based on the use of high-porrt compounds, with measurements obtained using highly controlled methodologies, in the real world of hazardous materia! sites, Ksp Constants can only be used as a reference when inferring leachability of these compounds from soil,, solid materials, waste, ami other media. Nevertheless, they do allo w for some prediction as to the -stability of reagents and end-product with respect to various conditions, characteristic, treat ent, and extraction fk d- hased test methods. [0023] from; the published Ksp values, it is evident, that the- intended end-products of the described invention, in particular, mercury sulfides, ve extremely low solubility in water. It i aiso evident that the reagents of the reagent system provided in this invention are very soluble relative to other prior art reagents and end-products, thus allowing for the invention, reagents to efficiently react with: problematic constituents as discussed herein. For example, calcium's high affinity for phosphate, as evidenced by the low solubili ty product of the formed compounds (calcium phosphate and related family salts) make calcium phosphate a poor choice for a reagent for the remediation of mercury. The calcium ions and phosphate ions in such systems are effectively combined and therefore, removed from competing with the mercury and sulfide reactions that form .mereury-sulfide end- roducts. This problem is avoided .by the presen inventi ^' on, which uses trisod uro phosphate in combination with calcium sulfide- -where - the- provided phosphate preferentially reacts with and binds the calcium from the CaS, and the sulfide is released to react with mercury .

[0024] Additionally, TNaP readily forms an alkaline solution with water. This feature of the specific phosphate reagent is important to the mercur -sulfide reaction end-product It -enhances controlled, non-mercury metal lie-hydroxide formation, and prevents the .formation of acidic conditions that are conduci ve to the generation and release of toxic hydrogen sulfide gas from the sulfide provided by the binary reagent system. The .highly soluble Thi&P releases phosphate ions when i ^' a solution, and these ions will react, with, other non-mercury heavy metals, but in particular, _, ^' calcium. If the phosphate-eontajning reagent were provided in the form oftricaicium phosphate. Triple Superphosphate, phosphate rock, or e forms from, this family of phosphate salts, the reae ants would not readily _. allow rel ease of phosphate ions to react with calcium from, the calcium sulfide. And. if phosphate is added in an acidic form., for example phosphoric acid, or under acidic conditions, the formation of hydrogen sulfide gas released from the CaS would render the system unsafe for use and release sulfide ions that would otherwise he available- to react with mercury.

[0025] Prior ait efforts to remediate mercury using calcium sulfide and a phosphate source teach -mat the addition of lime, hydroxide, or other alkaline additives or buffering compounds such as calcium carbonate are also required as separate reagents to elevate or otherwise control pH. The TNaP di sclosed .in this -process accomplishes .controlled pH adjustment without the need of an exogenous source, of hydroxide Ion. Furthermore, the disclosed, reagent system effectively treats le ehahle mercury without causing overly alkaline conditions that facilitate the formation of soluble mercury sulfide complexes/bisulfide forms (e.g. BgH.S ^2' , HgS(H ₂ S) ^2" ₅ llg(BS) ³ ; and/or HgS(HS) ^2" - Clever 1 85/Piao 2003), when the disclosed ratio range of CaS and TNaP is properly blended and applied to the .mercury contaminated material in a sufficient amount in view of the mercury content of the soil. ^' Fhe phosphate provided by the present invention's use ofTNaP reacts with the calcium supplied by the calcium sulfide (and available calcium that may already he within the waste material being treated) so that such calcium is not free to compere wit mercur for the sulfide. Other convexiilorj.al phospfaate-suppljdag reagents provide calcium to the -reaction process, thus- providing more unfavorable competition to mercury for the sulfide. With the present invention, the phosphate is provided with sodium, and not calcium, and sodiu does not compete for free sulfide or phosphate.

[0026] Water ca be added to the material being treated in order to enhance contact of the sulfide reactant with rnereur , facilitate mixing, lubricate waste particles to improve reagent dispersion throughout the target matrix, increase the mobility of !eachable mercury forms to better react wit the sulfide, control dust, and or to activate TNaP to its soluble alkaline condition.. Water addition requirements are primarily a function of the characteristics of the material to be treated. Extremely dry material, will require more water, and fully saturated sediments or slurries, for example, may not require any water to be added.. For typical soils, a moisture range of 5-12% is ideal and water .should, be added to achieve, this minimal range. For excessively wet and saturated materials such as sludges, slurries, and sediments, facilities should be designed to stage treated material for containment -purposes and to allow it to drain and dry. In a severe-case high, level water content situation, the waste material could, he de watered prior to. or after, treatment using gravity or mechanical _. ewatering means. In. such cases, treatability studies performed by those skilled in the -art will help optimize reagent .dosing and assess process cost with respect to where arid how operational dewatering would be most economically and productively performed.

[0027] in all processing eases, excess water beyond what is needed for the mercBry-sulf5.de reactions to proceed can unnecessarily dilute- the: reaetauts relative to the density of the waste material (and thus the mercury concentrations), and could potentially compromise the hi teachability of mercury from the end product. Excess water will also increase the mass of the treated end-product (and. increase t le cost of handling the end product) as well as create free- liqirids that are regulated with respect to material disposal at licensed, landfill facilities, making management and handling of the treated material difficult and problematic. Conversely, providing too little .water will prevent the reagents from: adequately reacting. -to form mercury of reduced teachability; TNaP may not be adequately dissolved and alkaline conditions not properly adjusted; calc-inm may not be removed, and the desired reaction between free sulfide and mercury s: thwarted: the mercury sulfide in the end-product may not precipitate out sufficiently within the contaminate material: or a combination of these or other iiaforeseeu. effects may compromise the desired results,

[0028] Another benefit of the present invention is thai water is not incorporated into the waste material mass via cementiiious, hydration, or po¾¾olanic reactions. As such, excess water is free to leave the treated mass by gravity drainage, mechanical agitation, _. eentrifugation, evaporation, capillary drying, or other physical means. This is of great iniportanee to large-scale

environmental cleanup and remediation projects where the treated, end-product must be transporte offsite and disposed of on a unit cost per disposed ton, basis.

[0029] ^' When a liquid solution of slurried CaS: and TNaP is desired for the treatment process application, calculated masses of each component can be added to a mixing container or tank, and makeup water added to prepare the de ired reagent solution concentration.. Heterogeneous mixing and suspension of the reagents with the water can be achieved b spindle, paddle,, o other suitable mixers in the tank, or by pump recirculation. The- pump can also, be used to deliver the reagent fluid to the waste in a waste-reagent mixer based on predetermined, dose

requirements for ^' batch mixing, or flow rates based on continuous mixer waste feed rates,

[0030] In anotiier highly effective reagent delivery method, dry reagents can be added at the proper ratio to the mixer via gravity feed from silos or elevated super sacks. Reagent addition, rates can be controlled via weigh cells integrated with off-loading- silo angers or conveyor belts, Super sacks can be held with a front-end loader or excavator equipped with a suspended scale system, load-cell, or integrated, with the equipment bucket hydraulics. In a. ver simplistic delivery method, prepackaged bags of reagents of known mass can be added to. the mixer manually. With these types of reagent deliveries to the waste and .mixer, w ter is added, preferably i ."the form of mutuall benef cial misting sprays that also mitigate dust from the contaminated material .and reagent during ^treatment Mending and mixing operations.

[0031] Further, and because the disclosed technology does not eanse or generate hydration reactions as would Portland cement or other such additives, process reactions do not. generate heat that would cause unsafe and. toxic releases of mercury vapor.

[0032] In the preferred embodiment, CaS and TNaP are supplied in a/nominal 1:1. ratio to each, other on. a dr weight mass basis. Each reagent can he added directly to the target waste individually, or in a combined blend. Each reagent or the combined blend of the two solids may be put into a slurry o sol tion mixture form, with water for that sl rry or solution mixture to be added to the waste material. Water may be added to facilitate dissolution of the reaetants in the reagent blend as a slum'., but at a. dose that, lso meets the minimal, need for the blending and reaction of the reagent blend 's reaetants with the mercury in the contaminated material.

[0033] With respect, to the dose rate or amount of each reagent, it is disclosed that a dose of 0,2% to: .2.5% for each is a preferred application. with, a combined dose of 0,4 to 5% on a 1 :1 reagent blend, weight to targeted waste weight

[0034] The 1 :1 ratio of CaS: TNaP may be varied to acconimodate .waste rfiateriai chemistry and raore broadly can range from 2:1 or J ;2, with the most effective: ratio to be determined on a ease- fey-case basis in view of the waste being treated, This ratio is highly important for controlling pH and excess sid.fi de conditions to preven formation of soluble mercury sulfide forms at ele vated pH, but also in acidic conditions common to landfill leaehaie. One skilled in the art of performing treatability studies will be able to identify the optimised reaction process within the prescribed, reactant dosage range individually and as a blend to the specific waste or solid material. [0035] The r ti o of 0.4% to 5% of a CaS- TNaP reagent blend to target materi al to he treated is an appropriate eagent blend, although a foil dose rate of 0.4 to 1.5 or 2% by weight is preferred, as this will ffliiiimize reagent cost, and treated end-product mass that may require subsequent transportation and disposal on a unit cost mass basis. In severe cases where the contaminated materia!, contains extremely high, levels: of mercury (e.g., 50 to ISO g Kg or higher), one may need to add sulfide in a molar amoun greater than ndicated by the stoichiometr of equations (1) and (2). This is particularly the case where the mercury is dispersed heterogeneously thro ughout the matrix .of the materia! being treated. Such cases m ay require a higher dose of the reagent blend to the material, and the ratio of CaS'TNaP may also require adjustment, in general, a 1:1 ratio of CaS;TNaP should ^' be- considered a theoretical minimurn.

[0036] The disclosed process will aggressively react with nrerciiry to form mercury sulfide, which has an extremely low solubilit product. As reported in various technical _, publications and literature, the K _ap of Mercury (11) sulfide is widely accepted to he 6.44 J 0. ^'33 , ^• .indicating that _. it is highly insoluble in water. While the solubility product constant of a compound is not always predictive of the insolubility or ieac.hability of that ^' com ound in acidic fluids, such as those used to evaluate waste for disposal it does suggest the HgS is extremely stable and resistant to disassoeiation, and that the reaction will proceed to the desired end-product quickly.

[0037] ^' To further ensure that die reagent system contacts mercury in the material being t eated, robust physical mixing of the waste with the reagents and water is employed. High shear mixing in a batch mixing chamber is preferred where mixing intensity and retention time during mixing will enhance .treatment results. Not only will reaeiants and mercury be more apt to be put in close-contact with each: other, but the particles f the waste coupled with the mechanics of the mixing blade shear cause elemental mercury droplets, to break, apart into units of higher surface area, increasing the droplets* reactivity. Droplets of elemental mercury are highly mobile as a result of gravity and mechanical forces. Th grindin of waste particles and abrasion caused by aggressive mixing: will serve to break u mercury droplets while keeping them oniformly suspended -within, the waste mass for reaction. Without high shear or robust mixing, mercury droplets could settle out of the waste mass and/or potentially agglomerate into larger extremel dense droplets, even to the point of a recoverable free liquid, in such conditions, mercur within the droplets might not adequately react with CaS and TNaP reagents, and settled merc r would fall outside of fee physical reach of mixer -paddies, preventing robust, mixing. With mixing, the combined surface area . of the droplets Increases, thus increasing the ability for mercury-reagent contact and reaction. The robust mixing requirement for the technology is best performed in a batch process where th mixing -shaft, paddles md blades are controllable -with respect to the rate and direction of rotation, and overall retention within, the mixing chamber. Reversal of the mixing shaft assembly will allow for prolonged mixing that rnay require up to 15-20 minutes for adequate mereury-to-reagent contact for the desired reaction to proceed to a desired, end-point

[0038] Other continuous feed-discharge type mixers soch as pugmills or brick mixers may also, be adequate, to achieve desired, mixing requirements; however such eqdpment tends to offe process operators less flexibility to accommodate waste material properties and process reactions variables. Batch mixers are also more capable of handling high water content is the material being treated. As water ..content increases, the reaetants are more likel to permeate various particles of waste and. debris carrying with, it the reaetants to -contact, with mercury. Batch mixers are designed to handle higher water/fluid content materials than pugmills or continuous flow- through mixing units. Crushed, concrete and bricks are prime examples of target material mat may contain mercury wdthin its interstitial spaces, where higher wate content and increased mixing time will improve the treatment of mercury within. When such debris types or particle sizes ai¾ encountered, the applicator of the techno lo gy may choose to pre-seree-n the niateriai to remove larger objects that might damage the mixing equipment, as well as any oversized materials not conducive to reagent penetration.

[0039] It is well knows. t¾at elemental mercury droplets are heterogeneous throughout, soil-like waste, given its fluid nature, high density, and ability to combine into large globules, or o breakdown to nearly in visible droplets. Mixing is essential to enhance the unifermity of mercury throughout the waste and replicate .the uniformity of reagent dispersion through the: matrix., Simple, single-pass-through mixi ng equipment may not pro vide adequate mixing needed to achieve the desired, remediation. [0040] In another delivery and .mixing method, rotating augers and .cutter heads ma be us d to _. vertically mix technology reagents m vertical soil columns from the ground sur&ce down to the bottom elevation of the contaminated soil, vertical limits. Overlapping -columns, (seeaat) will produce the most umTormly mixed material horizontall across a project site, with reagents delivered down the drill or Kelly shaft and outward to the mixing blades from the vertical, shaft center line to the extent of their outer diameter e tting and mixing path.. Suc in situ mixing equipment is designed to -deliver reagents and mix them with materials to be processed. The disclosed technology reagents aad reaction chemistry are well suited for in situ application to mercury contaminated material using this cosraon type of construction equipment, prov ided however, that subsurface obstructions and anomalies are identified and managed prio to the .start of treatment or when encountered.

[0041] An additional benefit of the binary reagent system provided by the invention is that it is well sffiied.for-ble mg.and SGkaig t)g for use in the emergency cleanup of elemental mercury spills.

E ¾B¾gles _. ggd€¾ m parativ e Studies

[0042] A number of experiments were carried out to demonstrate the effectiveness of the disclosed GaS/TNaP reagent system for remediating mercury in various samples, a d toeompaps the leachability performance of the invention with prior art method described in the literature. The _: results are summarized below in Tables 2-4, The treatability studies performed for the examples provided in this specification were performed on sample matrices obtained from site material samples. All materials were collected as grab samples and mixed as they were added o new and. clean S-gailon buckets. At the lab, buckets were remixed prior to each suhsanipling remo val of material, ah ^' quots for treatment application. The sample f om the former retort facility was obtained from archival material, but analyzed -at She tmie of the study to assure the

Characterization data was current

[0043] From the mixed sample bucket, 1 0. to 300g of sample matrix was placed into clean, labeled, and tared glass laboratory beakers using a top-load analytical balance sensitive to +/- 0.1g. Reagents: were added at the desired mass into decontaminated beakers and mixed for each treatment regime. Water was added in: similar fashion to facilitate mixing, taking care to avoid tree liquids, and to aid in the dispersion of the reagents tbro ug oat the sample mass. Mixifig was accomplished with a deeontaniiftated stainless steel spatula using both, folding and rigorous knifing action to achieve apparent homogeneity. Particular: attention to thorough mixing was paid w en elemental mercur droplets were evident within the matrix. Mixing was performed, for a typical period of 5-10 minutes to replicate field equipment performance. Upon mixing completion, treatment reactions were allowed to proceed tor approximately 1-3 hours prior to sohsampling and .plac ment into . containers for analysis by the third p rty laboratory, Edge Analytical, inc. of Burlington, WA,

[0044] For larger pilot study work, base sample matri was obtained from a batch .grout mixer at the site. Larger 1-2 Kg samples were then suhsarnpled as per above instead of the 100 - 300g sample aiiquots.

[0045] Table 2. Eia npleg 1 A ¾j¾c| jjg

Former Me cury Retort/ Heavy fV3eta§ Recovery .Site

.Example ^■ 1&

TotatHg fmg/Xg) 1080

T ^' CLP Hg (mg Q 11.35 33.35 0.010/ 0.0185

pH (S. U. i 8,55 10,21 9.5

CSS- ose { } 1.5 0.78%

T aP 1-5 0, 78%

Water Dose {%} 8% «%

Reagent Dose Rates - Dry wt. reagent percent to soil as sampled

TNaP ^■ = Trisodiurn phosphate

Data by Edge Analytical, inc., Burlington, WA

USEP Analytical Methods (7473A 1311, 9045D]

[0046] Examples I A and IB Illustrate the application of he disclosed reagents and their respective dosages to soil from a former mercury retort and heavy metal recovery remediation site using the preferred 1 : 1 ratio of reagents to each other along with water addition to the contaminated soil. In Example 1A, however, the: combined reagent dose applied to the soil was 3%, nearly twice that of Example J B. This resulted in an increased amount of leachable mercury from the untreated level. In. Example IB, the reagent blend, the blend dose to the contaminated material, and the water addition clearly identify the preferred ^■ embodiment as also supported by the duplicate analysis of the treated ead-produci . Noteworthy is the pH differential between Example 1 A and Example I B samples. Th fl of Example 1A pH is 10.2,1— more than half a standard unit above that of Example IB. In addition, tile amount of sulfide used in Example 1A is nearly twice as much as in Example IB,. The results for Example 1A are consistent with th problem of increased mercury solubility resulting from the use of excess sulfide in overly alkaline conditions due to the common ion effect as referenced in the prior art The pH of Example I B was a result of the controlled addition of the preferred reagent system of this invention assuring that neither excess sulfide nor overl elevated pH conditions were created. It s also noted that the overall mass increase of Example IB was less than 10%, of which nearly 8% as water that could he lost by dewatering efforts: after treatment, and less than. 1.6% was sourced from, the reagents t emselves.

[0047] With respect to the calcium sulfide used In the study (7/27/201¾ it was sourced. from bulk material that was in storage for over 48 mouths since its Material Safety Data Sheet (MSDS - 6/17/20.14} was prepared and provided with the materia! at the time, of delivery.

[0048 ] Most importantly, the disclosed invention exemplified hi Example IB and evaluated by U.S. EPA approved test and analytical methods met the KCRA limit for characteristically hazardous waste (0.2 mg/L) as well as the U.S. EPA. Land Disposal Restriction iirrsii (0.Q25 mg/L) for treatment of hazardous waste.

I S [0049] Table 3.. Vi»Mi¾ Treaimeat Results: C««ap«ri&g the Inv imn to the Prior Art

C ior Alkali Mercury CelS Site SoU - Viability Study Comparison

Total No.

Total Hg TCLP Hg Re _. &ge ^' nt-Systern Totai of 0.2 rng l ftC A <mg/Kgj pH (S.U.) {% wi. to Soil Dose.i%] Reagents limit iPass Fa!O

Untreated 16,863 1.94 6.50 - - Fail

V-1 0.099 CaS: 0.786% 1.58 Pass

TNaP: 0.798%

V-2 0.117 3.61 CaS; 0.77% 1.32 Pass

T aP: G.55%

y-3 0.140 9.31 CaS; 0.51% 1.38 2 Pass

TNaP;0.87%

V-4 0.209 9.S7 CaS: 1% 2 2 Borderline

TNaP: 1%

y-5 0.0581 12.44 CaS: 7.97% .15.65 3 Pass

Ca(0H} ₂ : 6.93%

H ₃ P0 ₄ : 0.75%

V-6 0.0321 NR CaS: 6 15.78 4 Pass

a?{ H) _? : 6%

CaC03: 3%

Η,ΡΟ,: 0.78%

V-7 1,3 13.30 CaS: 6% 12.2 3 Faii

Ca(QH¾: 5.5%

H ₃ P0 ₄ ; 0.73%

v-s 8.26 8.10 CaS: 0.1% 1.2 3 Fail

CPS: 0.8

TNaP: 0.3%

V-9 2.18 8.40 CPS: 0.6 l.S 2 fail

Ca(OH} ₂ : 1.2%

V-10 2.77 9.33 CPS: ^' !% 1,2 2 Fall

Ca{OH) ₂ ::0..2%

CaS: Calcium Sulfide

TNaP: Trisodiifm phosphate

Ca(OB) _? Caiciuro hydroxide

CPS: Calcium poiysulOde

KjPO*: Phosphoric Acid

- sx; result

^' Data by Edge Analy ica inc., Burlington, WA

USEPA Ana iytical Methods (7471A, 1311, 904SD;

[0Θ50] Table 3 presents viability treatment study results using the deseribed invention (V-1 through V-4) and other reagent-systems derived fr m the literature and prior art (V-S through V- .10). The data show th t the present .mvefitioix roviding calcium sulfide and irisodmrn phosphate resulted in the treatment of leaehahle mercury to below the IlCRA x it limit for hazardous waste. Regime V-l, followed a near 1:1 reagent ratio of 1 : LOS (CaS: TNaP), with V-2 and V-3 reagent ratio's inversed to each other at 1.4:1. and 1 ,71 :1, respectively. One skilled in hie art will know that these ratios can fee flexible, but dependent upon the chemistry of a specific contarairiaied material the level and type of leaehahle mercury present, etc. For the

contaminated materi ai treated in this stud , the reagent ratio range of 1 : 1.4 to 1 ,7:1 was adequate to achieve the TCLP mercury treatment <0.2 mg/L RCRA limit at total reagent dose to contaminated material of <2%. It is noted thai ¥-4 was a borderline failure. .At a 2% reagent- system dose to contaminated material using a reagent ratio of 3 ; 1.05, a pH of 9.97 S.U, resulted. As evidenced with the V-2 and V-3 treatment, TCLP mercury fluctuations were generated that would have likely facilitated passing result had the ratio been slightly adjusted to favor CaS over TNaP.

[0051] It is also noted, that the V-4 total reagent-system dose rate of 2% or even higher would be ap ropriate if total mercury was more elevated, and the mole ratio of -available sulfide did not provide adequate sulfide to react with moles of mercury in accordance with the 1 :1 mole ratio of the Hg + S ^"2■ → HgS reaction. With the present invention, the ratio of reagents in. the reagent- system can be adjusted to control the pH of the material during treatment so thai that excess suii.de does not cause an increase in mercur leacliaMHty as a result of an. overly alkaline pE. As previ o usly mentioned, the chemical characteristics of the contaminated m aterial will hav a direct impact on pH changes as a result of the ratio -of reagents in the reagent-system, and one skilled in the art will ascertain whether the pH of the processing during treatment is too elevated as identified during treatability process optimization studies, or if additional sulfide is required to accommodate the level of mercury present i the contaminated material

[0052] Treatment regimens ¥-5 through V-S provided more three (3 ) or more reagents to treat teachable mercury as teamed from prior art and the literature. These reagents were selected from ^' the list oh calcium sulfide, calcium hydroxide, calcium carbonate, and phosphoric acid. While V-5 and. ¥-6 both resulted in passing TCLP mercury results, V-? and V-8 failed to achieve the treatment objective.: V-5 and V-6.both contributed over 15% of the contaminated material mass in reagent weight to -the final end-product. If applied at fell-scale, both of these system would Siave increased treated material transportation and off-site disposal costs by this amount as well. Further, the additional reagent delivery, handling, dosing and mixing, and the final mass of the ead-prodact - would have other ated, cost increases, such as the time and cost, to load transport vehicles* unlike the reagent-system of this invention. In. the event, these regimes were to be applied to soil using in situ delivery .and mixing means, substantial soil expansion would result from treatment. _. .causing major civil engineering Implications and costly management

requirements for the increased, mass of materia! In situations where treated material would be left OTisite, or excavated and subsequently managed.

[0053] it Is also noted that V-7 had the same general treatmentrea ent-system applied as V-6, but without .calcium carbonate. The data illustrates the need for ibis fourth reagent as provided in V-6 where TCLP mercury met- the. treatment limit, and V-7 was over twenty-five (25) times the V-6 result, and almost seven (7) time the EPA CRA. limit of 0.2 mg/L for mercury in TCLP extract While the contaminated material mass would increase to a lesser degree than. V-5 or V- 6, V-5 would still have similar cost implications as discussed above with a mass increase of over 12%.

[0054] Treatment V-8 provided a three (3) reagent-system, consisting _: of calcium. sulfide, calcium polysnbj.de, and trisodi urn, phosphate at very low individual reagent doses i a .ratio of approximately 8:1 :0.375, respectively, with a total reagent-systeni dose to contaminated material of 1.2%. in theory, the sulfide provided by the calcium sulfide, and the calcium, polysuifide would be adequate for formation of -mercury sulfide at the near neutral pH of 8.26 -S.U . as suggested in V-l through V-3. Conversely, the increased amount of ealcium. rovided fey these two reagents of the system was ei ther consumed by the limited amount of phosphate added, and the remaining sulfide was not fully released, or the sulfide was converted to non-reactive sulfate, sul&r and sulfite species as a result of oxidatkio/redactioii reactions within the system. Further study is needed to examine this result, bu regardless, this reagent-system utilized three

(reactants) at a low close, and failed to yield the desired treatment limit,

[0055] Reagent-systems V-9 and V-1 provided calcium poiysulfide with calcium hydroxide to evaluate the efficacy of this system without phosphate and at a total reagent dose rate of <2%. While TCLP mercury results of 2.18 and 2.77 mg/L at pH levels of 8.40, and 9.33 S.U,, respectively, were lower than the resul of V-8, V-09 and V-10 both still failed to achieve the

2.1 ^• RCRA limit for leachable mercury, even with a reduced dose of sulfide provided by the system in moderately alkaline pH conditions, ft ss likely that the level of caleiiira provided b the applied reagent-system could be part of the cause. Regardless, and in consideration of the .results, the present invention- binary reagent system of calcium sulfide- and trisodium phosphate met the treatment objective for leachable mercur , while reagents, reagent combinations, controlled pH, and competitive dose rates identified in prior art did not.

[0056] In a less preferable embodiment, calcium sulfide can be replaced with calcium

poi.ysulfide (lime sulfur; CaS _H ; "CPS ^' ") , While the process may still perform as intended with proper control, CPS contains higher quantities of nou-snifide sulfur constituents such as sulfates and sulfites, and the reactive sulfide is in a less concentrated form than calcium sulfide. Further, and because of the need for additional sulfide -due- to the presence of undesirable sulfur forms and the elevated pH of the reaciant, the common ion effect described by Clever (1985), U.S. EPA (1997), and Piao (2003) from overly elevated alkaline pH conditions cause mercury- solubility issues. When more sulfide is required to adequately react with mercury, the increased dosing of CPS will also increase the pH of me contaminated material without the ability to control it with just CPS An. additional acidifying reagent would, tnen be required to neutrali e alkaline pH conditions, increasing the risk, of generating hydrogen sulfide gas.

CPS-g 3.3 1.3 4.60 1.74 Fail

CPS; Calcium poiysulfide

TNaP: Tnsodium phosphate

Ca .OM} ₂ ; Calcium hydroxide

H ₃ PQ ₄ . Phosphoric Acid

Data by Edge Analytica l., Inc., Burlington, WA

USEPA Analytical ethods (7471A, 1311, 9Q45D)

[0058] Examples CPS-1 to CPS-8 illiistrate the use of a calcium poly sulfide (CPS)-based reagent system for soil containing elemental .mercury obtained ^' from a former chlor-aJkali mercury cell soil site. While CPS- 1, which i luded trisodruffi phosphate nd cajciutn polysd_.de at a total reagent dose of 2%, achieved passing TCLP merewry resi.l½, the duplicate sample from, the same treatment failed. All other CPS-hased examples also failed. The failure of the replicate sample of this treatment regimen suggests that CPS does not provide necessary ^■ consistent results.

Consideration of varying dosages of CPS and with calcium hydroxide md phosphoric acid was attempted to provide more continuity with a CPS~phospha.te system for this specific

contaminated material based npors pif of the end-product. Results show tha mercury

leacha iiity was increased as a ^' result Collectively, the data shows the inconsistenc of results and unreliability of using a ea cium polysu!fide trisodinm phosphate reagent system, as opposed to the calcium sulfide/trisodium phosphate reagent system of the present invention.

[0059] llpofi _: reading this disclosure, other embodirneirts and modifications may be apparent to the skilled person. For example, in an alternate embodimen , the calcium sulfide (CaS) in the described ^' binary reagent system may be replaced with, sodium sulfide (Na^S), w ir the amount of TNaP adjusted as needed for p£T control and to account for any calcium that may be present in the host contaminated material. The present invention is limited only by the appended claims and equivalents thereof.