Land Contamination: Technical Guidance on Special Sites: Acid Tar ...

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Dispersing by Chemical Reaction (DCR)• This process works by using hydrophobic calcium oxide mixed with organiccomponents. The non-aqueous components of the acid tars are selectively adsorbedwithin the calcium oxide, and the water content of the acid tar reacts with the calciumoxide to give fine powdered calcium hydroxide. The contaminant is therebyencapsulated within this system, being water repellent and leaching resistant;• as for other neutralisation processes, DCR treatment can be applied with the materialexcavated and placed in layers, and the proprietary calcium oxide added usingmechanical equipment. However, this could have a significant space requirement.Alternatively, direct addition may take place in situ, provided that the tars are suitablyshallow. The resultant material can potentially be used as fill (subject to leachingtests) or for road construction;• there are several technical limitations to the process, including uncertainties regardingits permanence and the leachability of the treated material;• operational constraints could include the area required for treatment and requirementsfor control on emissions, together with significant health and safety issues raised bythe exothermic nature of the reaction;• the durability of DCR treatment is likely to be better than for stabilisation techniquesbased on cement. This is because, for DCR, the oils can be pre-distributed through thecalcium oxide prior to effecting the hydration reaction, thereby eliminating oil as aliquid phase. The hydration reaction forms calcium hydroxide, which has a highspecific surface area. The oil is adsorbed onto the hydroxide in molecular thicknessand this is considered by some to be virtually irreversible short of dissolving thecalcium hydroxide substrate (Grajczak (1995));• in the above reference, mention is made of application of DCR to acid tars in Germanywhere the subsequent product was disposed in an unlined cell and with apparently nodetectable contamination in groundwater some 15 years later;• in contrast, approaches based on cementation normally aim to produce a monolith withoil held as liquid phase droplets within the cementitious matrix. In this case, the longtermintegrity depends on that of the matrix.R&D <strong>Technical</strong> Report P5-042/TR/04 36
Box 6.1 Example of Remediation of Acid Tar Sludge by DCR Treatment(Grajczak, 1995)Acid tar sludge from the former Sinclair refinery site in Texas (a Superfundsite) was treated by the DCR process using a specially commissionedtransportable treatment unit handling 180 US tons/hour. 137,000 cubic yardsof waste (about 100,000 cubic yards of which was classified as acid tar) wastreated in total. The stabilised waste was then disposed of in a landfillconstructed on site to legislative standards. The treatment technology initiallyspecified was incineration unless it could be proven that a solidificationtechnology would be as effective. As site characterisation showed thatneutralisation would be required to reduce sulphur dioxide emissions, thisprompted detailed study of solidification/stabilisation technologies as analternative to incineration.Most of the waste, particularly that deeper in the pits, was in the form of slowflowing, viscous tar. Bench scale trials were conducted by vendors againstestablished treatment goals (expressed in terms of parameters such ascompressive strength, liquid release, and leach testing). Followingexamination of these and evaluation of tenders, a tender based on the DCRprocess was selected. The treatment unit comprised a waste crusher/feedsystem, a reagent feed system, an emissions control system and two paralleltreatment trains (hoppers, mixer, reaction chamber). Emission control wasrequired as the initial reaction is exothermic and dust and VOCs needed to becaptured and treated for a minimum of 30 minutes following waste-reagentmixing. This comprised a hydrostatic precipitator for dust, a packed spraytower and activated carbon for organic vapours.The material produced was described as homogeneous, dry, free-flowing, easyto transport and readily compacted in the landfill. It is similar to natural claysbut without the affinity for water. The period from conceptual engineering tostart-up was 12 months and the treatment period was 13 months. The projectwas reported by the above author to have been concluded successfully.Other Processes• Other processes include several involving solidification, similar to those used for thesolidification of sewage sludge;• two processes have been piloted in Germany with some success, one of whichproduced a solid concrete-like material and another produced a powder. However,certain problems were encountered, most notably the need for large quantities ofbulking material (580 kg were needed to solidify 25 kg of acid tar). This could lead todisposal problems due to the large amount of space required.R&D <strong>Technical</strong> Report P5-042/TR/04 37
Page 1 and 2: Land Conta
Page 3 and 4: CONTENTSFOREWORDiGLOSSARYii1. Intro
Page 5 and 6: FOREWORDPart IIA of the Environment
Page 7 and 8: CresolsCreosoteDCRDesorptionDesulph
Page 9 and 10: PVCRCRASelosafeSodium saltsSodium h
Page 11 and 12: 1. INTRODUCTION1.1 BackgroundThis r
Page 13 and 14: SECTION 2: INDUSTRIAL PROCESS/FACIL
Page 15 and 16: 1.5 Linkages Between the Gu
Page 17 and 18: 2.1.2 Overview of acid tar lagoon s
Page 19 and 20: Overall CommentsAcid tars can be of
Page 21 and 22: White Oil• Acid tar lagoons from
Page 23 and 24: Box 2.5 Scenario: Acid tar disposal
Page 25 and 26: 3. CHEMICAL AND PHYSICAL CHARACTERI
Page 27 and 28: Table 3.1 - General Physical Charac
Page 29 and 30: The chemicals listed in Table B.1,
Page 31 and 32: 4.2.3 Common mistakesIt is possible
Page 33 and 34: Geophysical methods, such as resist
Page 35 and 36: Investigation locations will need t
Page 37 and 38: • gas chromatography by simulatin
Page 39 and 40: 5.2.2 Water environmentThere is lit
Page 41 and 42: 5.3 Assessment of Investigation Dat
Page 43 and 44: 6. REMEDIATION ASPECTSKEY QUESTIONS
Page 45: 6.2.5 Solidification and stabilisat
Page 49 and 50: 6.3 Natural AttenuationNatural atte
Page 51 and 52: Table 6.1 - Remedial Options/Techni
Page 53 and 54: Table 6.2 - Remedial Options/Techni
Page 55 and 56: 6.4 ValidationThe principles of val
Page 57 and 58: • all personnel should follow a d
Page 59 and 60: Verschueren (1983) Handbook of Envi
Page 61 and 62: USEPA. Innovative Site Remediation

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