lime remediation using quicklime

1 Table 2 Precipitation of Anions using Lime,Optimum pH Values forPrecipitation and Achievable Residual Concentrations(1)HistoryLime Stabilisation treatment of contaminated soils laden withhazardous waste is a tried and proven chemical fixation the technology and its acceptance has progressed dramaticallyover a number of years as a simple,cost effective and flexibletreatment method for remediation of soils and recycling them back tousable contaminated sites operated by both government andprivate industry have been returned back to usable land using limestabilisation treatment projects have been completed in the areas of soilscontaminated with metal wastes,oily wastes and chemical recently the technology has found application in ratifyingharbour dredge material during the construction and improvement ofchannel ways (2).A number of projects have also been carried out successfully in the UKand Europe,including remediation of the ICI Explosives site at Ardeer inScotland (4) and at Ulverston Tannery in Cumbria (5).

2 More details areavailable in the British Cement Association and British Lime AssociationIndustry Guide [7].Lime stabilisation technology has been evaluated in-depth by the USEnvironmental Protection Agency (EPA) as part of the SITE program(3)(Superfund Innovative Technology Evaluation) and now is included intheir treatment matrix for best available technologies based on costeffectiveness and capital remediation using quicklimeIntroductionContamination of land can take many forms,from solid items such asold boots and shopping trolleys,to land containing chemicals such asacids and heavy land will often give rise tocontaminated effluent or oily run off water and the chemical industry lime is one of the major chemicals used forenvironmental treatment of waste ability of lime toneutralise acids and react with heavy metals and many solubleimpurities,rendering them insoluble,is well use oflime to remediate contaminated sites combines this technology withequally established Civil Engineering techniques of groundimprovement and is known as stabilisation/solidification (S/S).

3 As can be seen from the data below(1),lime can effectively precipitatemany metals and other 1 A Graph of Metal Solubility Site InvestigationAs far as possible,the preliminary site investigation should identify the different groups of materials that exist on the site and the type(s) of contamination present[7] and [8].This investigation can be carried out by a number of MethodologyThe treatment methodology will vary depending on the nature of the contamination and the physical state of the contaminated the next section wewill cover the different types of wastes [7] and [8].Solid WasteContaminated land or industrial sludge/wastes that are hazardous due to toxic contaminants,especially heavy metals are mixed with lime to form insolublecompounds,which are these sludges can be de-listed,that is,classified as non hazardous and disposed of or re-used without further treating hazardous wastes lime,Portland cement,fly ash,or a mixture of these materials are often waste is evaluated in the laboratory,first treated withsufficient lime and then solidified with mixtures that form pozzolanic compounds are mixtures of lime and materials like fly ash,which makea cementitious material when mixed gives structure and strength to the treated material so it can be used as an engineering fill material or as a rawmaterial for a recycled can often be achieved using readily available equipment.

4 Such as rotivators and piling - Treatment is usually undertaken on site in maximum 300mm deep layers of contaminated is spread and mixed at the required Equipment - Treatment is usually undertaken on site, using the Piling Rig to create an overlapping network of treated columns,which will either cover the area(Fig 3) or form a "protective wall" around the Columns - usually large diameter (>500mm) columns of lime / soil are installed in situ by means of a special auger that bores the hole,then as the auger is withdrawn,injects and mixes the lime (normally 7-10% by dry mass ofsoil) with the soil and compacts the or other binder can be added where hot spots can be remediated using anoverlapping network of limetreated piles to ensure remediation of Contaminated + <2<3 Amphoteric above pH , formation ofhexahydroxochromiteabove pH > <2<100> <2< , formation oftetrahydroxozincate above pH - - +Cr3+Fe3+Fe2+Zn2+Pb2+Ni2+Cd2+Optimum pHforprecipitationResidualconcentration inmg/l after limeprecipitationStatutorylimits mg/l inEuropeSpecial featuresOptimum pHforprecipitationResidualconcentration inmg/l after limeprecipitationSO43+F+PO43+Anion2-4> <200020 - 70<1 Table 1 Residual Metal Ion Concentration inwater which can be Achieved by means ofOptimum pH Regulation(1) 24193_bla_Tech4_lime 29/9/06 1:57 pm Page 1datatechnicalBRITISH LIME Lime Association Technical Booklet.

5 "Lime for a Clean Environment - Lime and dolomite Products for the Treatment of Drinking Water,Waste Water and Sewage Sludge." Robinson ,Singleton Birch."Lime remediation of contaminated soils - The Quick Technology." EPA Superfund "Case Studies available via the US EPA website " Barker P."Case History - Land remediation at ICI Ardeer." B." remediation and ground improvement at Low Mill Tannery (Ulverston)." Lime Association Datasheet Series 1."Earthworks improvement using quicklime ." of Brownfield and Lime Industry Agency and CASSST - Guidance on the stabilisation/solidification for the treatment of contaminated land. BRITISH LIME ASSOCIATIONG illingham House, 38-44 Gillingham Street, London SW1V 1 HUTel 020 7963 8000 Fax 020 7963 8001email British Lime Association is one of the constituentbodies of the Quarry Products Association,the tradeassociation for the aggregate,asphalt and ready-mixedconcrete WastesIn the treatment of leachate (aqueous solutionscontaining chemical contamination which can includeheavy metals such as lead,cadmium,zinc,copper,arsenic,etc)

6 ,lime is used to adjust the pH of thesesolutions to precipitate insoluble hydroxides andcalcium complexes of these ,the waters are safe for disposal and thesludges are chemically fixed,safe for disposal,transport and WastesNon hydrocarbon oily wastes can be successfullytreated with lime to form insoluble calcium soaps,which are non-leaching,this is a non-reversiblereaction called saponification (otherwise known assoap making).However,there are pitfalls that occurthat one must be aware of and these can have adetrimental effect on completion of the process andrendering of the oily addition of dry lime to an oily waste will simplysoak up the water and oil but not react to forminsoluble one takes this dry treated materialand compresses it,liquid will be squeezed out of is not yet a stabilised properly treat oily wastes,a lime slurry is used -and preferred temperatures around 50 to 70 these temperatures a saponificationreaction occurs quite rapidly forming Calcium saponification reaction is not astructural material is desired,then sand or soil is mixedwith the soap to give it materialscan also be mixed with the soap/sand mixture to forma cement like material with considerable Hydrocarbon Wastes(PCB's,Dioxins,Pesticides,Herbicid es)

7 For some years the US EPA has listed the use of lime as anacceptable way of solidifying and stabilising solid wastes ladenwith PCBs,Dioxins,Pesticides and is an acceptablecontainment treatment method with the lime-stabilised materialultimately being incinerated (1500 - 2000 C) at a later date(3).Associated UsesLime chemistry is very useful when remediating contaminatedland,but It's applications are far wider when the entire projectlife is contaminated sites can require treatment of the area toreduce moisture content and increase load bearing capacity toallow traffic movement before remediation work can commence,this can be easily achieved with lime improvementtechniques(6).Treatment of any leachate to remove solublecontaminants can usually be achieved with remediation of contaminated land is a simple process,which uses readily available machinery to give a cost effectivesolution and can be done in-situ,which reduces further details on lime remediation of contaminated land,please contact the British Lime Association onTel:020 7963 8000 Fax:020 7963 29/9/06 1:57 pm Page 2