Quicklime Treatment Research Articles

Successful large-scale and long-term kelp forest restoration by culling sea urchins with quicklime and supported by crab predation

In 2013, a large scale (70 hectare) kelp forest restoration experiment was conducted in a sea urchin barren that had been stable for 45 years. We used 200 tons of quicklime to eradicate the sea urchin population. Kelp recovered within a year in the lime-treated sites. Quickliming did not significantly affect the abundance of non-target species. Mobile kelp fauna colonized the restored kelps, but at a slower rate than kelp and other macroalgae, probably due to slower dispersal abilities. The monitoring period (2012–2021) encompassed the expansion of invasive red king crabs, which emerged as a novel predator of sea urchins. This led to a gradual decline in sea urchin populations and facilitated kelp recovery also in the control sites. This delayed recovery does not invalid the conclusions of the short-term efficiency of the quicklime treatment, but it makes it difficult to conclude about the long-term effects. The study shows that quickliming can initiate kelp recovery within large urchin barrens. We postulate that the recovery of kelps outside the limed areas was due to crab predation, and that successful kelp restoration in areas with recruitment of sea urchins depends on a persistent top-down control of the urchins.

Effect of liming on polycyclic aromatic hydrocarbons leaching from hydrocarbon-contaminated tectogenic industriosol

Soil stabilization/solidification is commonly employed remediation method for contaminated soils. Until now, limited attention has been given to the application of quicklime in polycyclic aromatic hydrocarbons (PAHs) contaminated soil. We treated a tectogenic industriosol spiked with 50 mg kg−1 of four PAHs (12.5 mg kg−1 each of fluorene (FLU), phenanthrene (PHE), fluoranthene (FLT) and pyrene (PYR)) using three different liming agents at 1% (w:w): quicklime (CaO), hydrated lime (Ca(OH)2) and carbonate calcium (CaCO3). All treated samples were leached in water at a solid-liquid ratio of 10, with subsequent analysis of leached soil and leachates for PAHs content. Results revealed that the addition of liming agents led to a reduction in FLU and PHE concentrations in treated soil by 6.81 ± 2.47% and 28.88 ± 4.18%, respectively, compared to a not-treated sol. However, no significant impact was observed on the 4-cycles PAHs (FLT and PYR). The addition of liming agents also significantly decreased the amount of PAHs in the leachate, by 100% for FLU and PHE, and by 74.9 ± 17.5% and 72.3 ± 34.8%, for FLT and PYR, respectively, compared to not limed soil. Among the liming agents, quicklime was the most effective in reducing the amount of 4 cycles PAHs in the leachate. Various mechanisms, such as encapsulation, volatilization and oxidation could contribute to this observed reduction. Quicklime treatment at a concentration of 1% w:w in PAHs-contaminated soil emerges as a promising technique to effectively reduce PAHs concentration in soils and mitigate PAHs mobility through leaching. This study also sheds light on the possibility to limit CO2 emissions and resources exploitation to assure the remediation process, thereby enhancing its overall environmental sustainability.

Potato (Solanum tuberosum L.) cultivars physiological, biochemical performance and yield parameters response to acid mine water irrigation and soil physiochemical properties

This paper aimed to analyse the potato cultivar’s response to physiological, biochemical performance, yield parameters and soil physiochemical properties when subjected to quicklime (un)treated acid mine drainage (AMD) irrigation. A randomized design experiment was conducted with five water treatment levels: TW1; TW2; TW3; TW4 to TW5 replicated four times. The results showed that the quicklime treatment increased the pH of the AMD water, reduced the concentration of EC, NO3−, SO42− and ameliorated heavy metals. However, unsafe levels of heavy metals above the maximum permissible (WHO/FAO) levels were found in Pb, Mg and Mo for water (TW4 and TW5), while As, Cd and Cr for soils (ST4 and ST5) respectively. For potato tubers (TT4 and TT5) concentrations of As, Cd, Cr, and Pb were above the maximum levels. Stomatal conductance, chlorophyll content and yield parameters responded positively by increasing significantly on TW4 and TW5 treatments, but negatively (reduced) towards TW2 and TW3 treatments. A higher bioaccumulation factor was obtained for Zn ˃ Cu ˃ Mg ˃ Pb ˃ Mn, which was an indication of the contamination status of soil, with Zn being more concentrated than other metals. The findings indicate that quicklime-treated AMD is usable for potato irrigation with regular monitoring of heavy metal levels and strict observation of water reuse protocols. The use of this large source of ameliorated (AMD) water will go a long way in improving food security in South Africa and/or in countries where agriculture production is around mining areas.

Experimental study on water transfer mechanism of quicklime modified centrifugal dewatering clay

This study investigates the water transfer mechanism of quicklime modified centrifugal dewatering clay. A small-scale centrifuge device was used to investigate the change of bound water content in modified clay under different laboratory test conditions including quicklime content and curing age, and analyze the water transfer mechanism in the process of quicklime treatment, and its impact on clay properties. The results show that the content of pore water decreased by 6.2% ∼ 16.9%, the content of bound water increased by 4.2% ∼ 12.9%, and the content of hydration water increased by 6.1% ∼ 14.1% due to hydration reaction caused by the quicklime. The increase of quicklime content facilitates the conversion of free water into bound water and hydration water in a relatively short time. The pozzolanic reaction occurs on the surface of the clay particles to absorb free water and convert it into bound water, while part of Ca (OH)2 crystals generated by hydration reaction adhere to the surface of clay particles, grow into needle-shape and fibrous structures, and absorb free pore water and convert it into hydration water. For field applications, the mixing percentage of quicklime is recommended to be below 9% by dry weight. From the cost perspective, 7-day curing age is recommended in the field. The essence of quicklime modification is to transform the free water with relatively low pF potential energy into the bound water and hydration water with relatively high pF potential energy. A schematic diagram of water transfer mechanism was also proposed in this study for quicklime modified clay and validated using the aforementioned experimental data.

Influence of the physical and chemical characteristics of sediment fillers on the properties of mastic asphalt

This study aims to optimize the integration of dredged sediments as fillers in formulations of hydrocarbon materials such as “mastic asphalt” for sealing applications. River sediments were collected from the Hauts de France region are the following ones: Aire sur la Lys (ASL), Urban Community of Arras (ARS), European Metropolis of Lille (MEL), and Noyelles sous Lens (NSL) to identify the impact of integrating them in asphalt formulations. Pure asphalt mortars were formulated (AP1) according to the specifications. Asphalt based on limestone fillers have achieved mechanical performance set by the standards. It can be seen that MEL and NSL sediments have a limited use because of their high organic matter content and their high rate of Intergranular voids (RV), which leads to overconsumption of Bitumen. However the calcination of these sediments at 550 °C can remove the organic matter and give a better improvement in physical and mechanical performance than the quicklime treatment. Asphalt-based calcined sediment at 550 °C (NSLC) has been shown to deliver up to 80% improvements in the mechanical performance in comparison to the raw sediment mix. In addition, the use of a soft grade of Bitumen gave impressive benefits with the sediment fillers which can reach up to 23% substitution and reducing the quantity of Bitumen up to 19%.

Thermo-Chemical Treatment for Carcass Disposal and the Application of Treated Carcass as Compost

A mechanized thermo-chemical treatment system was developed to treat the undecomposed carcass and remediate livestock burial sites. Animal carcasses were thus processed via crushing, mixing, and treatment with quicklime treatment, heat treatment (200–500 °C), and mixing with sawdust. The machinery was applied to two sites where 16,000 chickens and 418 pigs had previously been buried in fiber-reinforced plastic storage bins. No dioxins were detected in the gas discharged during processing, and the concentration of total volatile organic compound, toluene, ethylbenzene, xylene, and styrene were 430.3, 139.0, 18.3, 21.4, and 10.4 μg/m3, respectively, which were below the air pollutant emission standards issued by the Korean Ministry of Environment. Korean standards stipulating the use of treated carcasses as compost (C, N, and P content, heavy metal concentration, Escherichia coli, and Salmonella) were met, but the germination index value was less than 70, not satisfying the criteria. Plant height, leaf length, leaf width, and dry weight of lettuce grown in soil amended with treated carcass product were significantly lower than those grown in low nutrient soil due to the poor germination index of the treated carcass. These results indicate that a composting process is required before the use of the treated carcass as a fertilizer. The addition of zeolite retarded the elution of ammonia from the carcasses and its efficiency was about 87.9%. It is expected that the mechanized thermo-chemical treatment process developed in this study could replace other technologies for the remediation of livestock burial sites.

Prediction of shear strength parameters in soil–lime mixture design – part 2: hydrated lime

In the field of lime stabilisation of soil, one of the main research objectives is optimisation of the mix design procedure. To this aim, correlations between strength parameters of treated soils and the main characteristics of lime treatment can be useful to have a preliminary estimation and reduce the number of laboratory tests to be performed in the design phase. This paper, part 2 of two companion papers, describes a comprehensive series of direct shear tests carried out on specimens of six soils with different characteristics treated with different amounts of hydrated lime (HL). In part 1, quicklime (QL) treatment is addressed with the same purpose. Good correlations between shear strength parameters and main soil–HL variables were obtained by multiple regression analyses and they were validated with data from the literature. The most significant predictors of the shear strength parameters were always found to be the clay fraction of the untreated soil and the lime content. In order to obtain an overall view of stabilisation possibilities, experimental results and predicted values for QL treatment formerly obtained by authors are discussed in this paper. This approach helps in the selection of the most suitable type of lime.

Prediction of shear strength parameters in soil–lime mixture design – part 1: quicklime

Lime stabilisation is a widely used technique, however, in practical applications, it is not unusual to encounter cases of failure due to a lack of consideration of all the steps involved and incomplete account of the variables to produce a successful mix design. This paper, part 1 of two companion papers, presents useful correlations between the shear strength parameters of compacted soil–quicklime (QL) mixtures and the main variables of lime treatment. In part 2, shear strength data of compacted soil–hydrated lime mixtures are processed for the same purpose. The correlations for QL treatment were derived from 26 triaxial compression and direct shear tests by multiple regression analysis. The database was constructed with experimental results concerning five soils with different plasticity characteristics and CFs. QL was added to the soils in different proportions. Tests were carried out at different curing times on soil–lime samples compacted at different water contents. Very good correlations were obtained and validated with data from the literature. Thanks to these correlations, the optimum lime amount can be preliminarily identified, knowing the characteristics of the soil to be treated and the required design shear strength parameters.

Effects of microwave, thermomechanical and chemical treatments of sewage sludge ash on its early-age behavior as supplementary cementitious material

To better inform the recycling of sewage sludge ash (SSA) in cement-based construction materials, this laboratory study investigated a variety of modification methods aimed at improving the value of SSA. For pre-treatment, three different methods of physical modification including low-temperature drying, grinding, high-temperature calcination were selectively performed. Microwave treatment was also explored as an alternative to the calcination procedure. Subsequently, chemical modification of the SSA was performed by blending with quicklime (QL) for likely chemical activation. The effectiveness of these treatments was assessed in terms of leachability of heavy metals out of the treated SSA and the reduction in total organic carbon (TOC). High-temperature calcination of SSA enhanced the immobilization of heavy metals (e.g., Mn, Zn, and Ba). In contrast, the QL treatment helped immobilize some heavy metals (e.g., Mn and Zn) but re-liberated other metals (e.g., Ba). Compared with calcination at 500 °C for 2h, 15-min microwave heating of pre-treated SSA exhibited better performance in immobilizing the heavy metals and nearly as good performance in reducing the TOC in the SSA Finally, based on the compressive strength data of the cement pastes, microwave treatment is an effective alternative to thermal calcination, in terms of mitigating the side effects of admixed SSA on the cement hydration.

Improvement effects of quicklime and calcium magnesium phosphate fertilizer on acidified soil cultivating Codonopsis tangshen.

To solve the problem of soil acidification in the cultivation of Codonopsis tangshen, laboratory experiments were carried out to investigate C. tangshen seed germination, seedling growth and soil exchangeable acid, microbial community structure after applying quicklime (QL) and calcium magnesium phosphate fertilizer (CMP). The results showed that QL and CMP treatments significantly improved the survival rate of C. tangshen seedlings from 147.7% to 326.7% and from 270.1% to 311.2%, respectively. The maximum increase rates of the height of C. tangshen seedlings were 516.7% and 546.3%, and that of root length were 798.0% and 679.2% in the treatments of QL and CMP, respectively. 1‰-4‰ QL or CMP treatments increased the relative chlorophyll content, antioxidant enzyme activity and the content of soluble protein of C. tangshen seedlings, decreased the content of malondialdehyde and superoxide anion radical of seedlings, increased soil pH by 0.88-2.02 units and 0.23-1.19 units, and decreased the exchangeable aluminum content in soil by 53.0%-95.3% and 17.6%-81.3%, respectively. Soil bacterial and actinomycetic abundances were significantly higher in 2‰-4‰ QL or CMP treatments than that in the control. Soil fungal abundance was significantly lower in the QL treatment of 2‰ and CMP treatment of 4‰. 1‰-4‰ QL or CMP treatments significantly increased fresh weight of C. tangshen tubers by 40.5%-78.5% and 28.4%-78.8%, respectively. In conclusion, the suitable quantity of QL and CMP for acidified soil (pH=4.12, ρb=1.15 g·cm-3, tillage layer=15 cm) amendment were 1.73-3.45 t·hm-2 and 3.45-6.90 t·hm-2, and QL and CMP amendment could fit the optimum soil pH (5.5-6.5) for the growth of C. tangshen seedlings.

Swine manure and quicklime have different impacts on chemical properties and composition of bacterial communities of an acidic soil

Red soil is a kind of Ferralic Cambisol. Good hydrothermal resources but usually acidic and low base saturation make it very easy to be acidified under unreasonable fertilizer managements in agricultural area. In 1990, a series of fertilizer applications were established on a homogeneous field to investigate the soil fertility changes under different fertilizations in Hunan province, among them, long-term chemical nitrogen fertilization (NPK) induced severe soil acidification, whereas long-term chemical plus swine manure fertilization (NPKM) exhibited an overwhelming advantage in terms of nutrient concentration and bacterial diversity. In 2010, to investigate the effect of short-term quicklime and swine manure applications on the acid red soil, a remediation experiment was established on the NPK treatment. Quicklime (CaO) and swine manure (the same as the swine manure in NPKM) applications on NPK soil had different effects on remediating the soil acidification: short-term quicklime application (NPK+Ca) increased soil pH and bacterial diversity more rapidly, whereas short-term swine manure application (NPK+M) improved soil nutrient concentration more effectively. Alteration of environmental conditions caused significant changes of bacterial community: oligotrophic groups were in greater relative abundances with quicklime treatment, whereas copiotrophic groups were in greater relative abundances with swine manure treatment. This study provides insights into the two major remediation approaches for an acidic red soil; these insights are important for soil remediating and improving fertility. Taken together, we recommended short-term quicklime application to increase the soil pH quickly and long-term swine manure fertilization to improve soil fertility.

Analysis of Hydrated Lime Consumption in Circumneutral Underground Coal Mine Drainage Treatment

Treatment evaluations were performed at four Pennsylvania hydrated lime treatment sites and one quicklime treatment site designed to remove ferrous iron from underground coal mine drainage. Two of the sites included a pretreatment decarbonation step to exsolve CO2(aq) and reduce hydrate consumption due to hydroxylation and calcite formation. Decarbonation reduced the daily hydrated lime dose by 22 % at one site and 28 % at the other. Field-measured CO2 mass transfer coefficients were determined for both decarbonation systems. CO2 mass transfer modeling predicted that Ca(OH)2 use would be reduced by an additional 19 and 28 % at these sites if the decarbonation systems were optimized. Hydroxylation of CO2 species and calcite formation consume between 40 and 90 % of the Ca(OH)2 dose. In terms of cost, more money is being spent on consumption due to hydroxylation and calcite formation than on removing the targeted parameter, ferrous iron. These processes can be minimized by improving decarbonation and oversizing ferrous reactor tanks to lower treatment pH.

Research on the Quicklime Treatment Dewatered Sludge Technology and Mechanical

The fundamentals of lime treatment for dewatered sludge and main factors which affect the treatment process are introduced in this study. According to the results, higher effective calcium oxide content in lime contributes to faster heating rate of the semi-dry system and better effects of semi-dry process. Sludge at the moisture content of 45%-55% after the semi-dry process can be well balled while that at the moisture content of 35% can easily get collapsed and has hard surface. Mechanical design parameters are determined by experiments. The optimum stirring time is 5-10mins when well stirred and the stirring rate should be slow. Heat preservation jacket is needed for the machine and the water vapor, which is produced by heating, should be exhausted in time.

Monitoring and environmental modeling of earthwork impacts: A road construction case study

This study presents the contributions of materials, earth engineering machines and construction techniques to potential environmental impacts from the main items of typical road earthworks. To achieve this goal, the overall activity at a 1.9-km long French earthworks project site for a heavily trafficked highway was surveyed during its 2007–2009 construction period. Using data collected and a numerical model of road life cycle assessment (LCA), i.e. ECORCE, six indicators could be evaluated, namely: energy consumption, global warming potential, acidification, eutrophication, photochemical ozone creation, and human chronic toxicity. When available, several life cycle inventories were implemented in order to appraise indicator sensitivity with respect to the considered panel of pollutants. Results also allowed estimating from an LCA point of view: (i) the conservation of both aggregates and soil as induced by quicklime treatment and (ii) the duration necessary for projected traffic levels to offset the potential environmental impacts of the earthworks stage.

Quicklime treatment and stirring of different poultry litter substrates for reducing pathogenic bacteria counts

Testing different management practices can help to identify conditions that decrease or even eliminate pathogenic bacteria in poultry litter. A trial was conducted to evaluate the effects of daily manual stirring (rotation of the litter with a pitchfork) for the first 14 d of a bird's life (WDR), in 3 types of poultry litter substrates and quicklime treatment (CaO) during layout time between flocks on pathogenic bacteria occurrence (cfu). A total of 216 male Cobb broilers were randomly allotted to 18 pens with new litter (experimental unit). A split-plot design, with 6 treatments allotted to the main plots, was used: 1) wood shavings (WS) + WDR, 2) WS without stirring up to 14 d (WODR), 3) rice hulls (RIH) + WDR, 4) RIH + WODR, 5) mixture of 50% RIH and WS + WDR, and 6) mixture of 50% RIH and WS + WODR. Two treatments were allotted to the subplots: 0 and 300 g of CaO•m(-2) litter. After depopulation, litter samples were collected, and CaO was incorporated into the litter in the designated half of each pen. The cfu from litter samples after 7 d of the quicklime treatment were counted on Chapman agar, brain heart infusion media, and MacConkey agar. The data were analyzed using ANOVA, and the means were compared by least squares means (P < 0.05). Neither the type of substrate nor the act of stirring affected the cfu. The incorporation of 300 g of CaO•m(-2) litter efficiently reduced the cfu observed on brain heart infusion, Chapman agar, and MacConkey agar media by 57.2, 66.9, and 92.1%, respectively, compared with control (6.4, 17.9, and 46.1%; P < 0.001). In conclusion, the incorporation of 300 g/m(-2) of quicklime in poultry litter reduces the cfu, regardless of the substrate and stirring performed.

생석회 처리가 토양 세균의 생존과 군집구조에 미치는 영향

When quicklime is added into soil for various purposes, abrupt changes in soil chemistry may affect essential ecological functions played by indigenous bacterial communities in soil. The magnitude of influence was estimated by observing changes in abundance and diversity of soil bacteria after quicklime treatment. When several soil samples were treated up to 20% (w/w) quicklime, plate count of viable cells ranged <TEX>$10^2{\sim}10^3$</TEX> CFU <TEX>$g^{-1}$</TEX>, showing a reduction of more than <TEX>$10^4$</TEX> times from viable counts of the untreated sample. Diversity of the bacterial isolates that survived after quicklime treatment was analyzed by conducting <TEX>$GTG_5$</TEX> rep-PCR fingerprinting. There were only two types of fingerprints common to both 5% and 20% quicklime samples, implying that bacteria surviving at different strength of quicklime treatment differed depending on their tolerance to quicklime-treated condition. Isolates surviving the quicklime treatments were further characterized by Gram staining and endospore staining. All isolates were found to be Gram positive bacteria, and 85.4% of them displayed endospores state. In conclusion, most bacteria surviving quicklime treatment appear to be endospores. This finding suggests that most of ecological functions of bacteria in soil are lost with quicklime treatment.

Pasteurization of chicken litter with steam and quicklime to reduce Salmonella Typhimurium

SUMMARYThe nursery industry pasteurizes soil with steam and quicklime to reduce plant pathogens. The mechanism of action for quicklime is the resulting exothermic reaction that occurs when the chemical interacts with water and its ability to increase pH levels. These treatments may also reduce pathogens in a commercial poultry house. In this study, a steam sterilization cart simulated conditions used by the nursery industry to treat litter inoculated with Salmonella enterica serovar Typhimurium. A homogenized sample of litter was exposed to steam for 0, 5, 30, or 120 min. Quicklime was used at concentrations of 0 (control), 2.5, 5.0, or 10.0%. All steam treatments, with or without quicklime, significantly reduced Salmonella Typhimurium colonization by at least 3 orders of magnitude. Significant reductions were also observed in the treatments with quicklime alone. Both the steam and the quicklime treatments often reduced colonization to undetectable levels, even when samples were enriched. Therefore, we demonstrated 2 novel techniques for reducing Salmonella Typhimurium in poultry litter. Soil pasteurization potentially offers an environmentally sound means of reducing the pathogens present in used poultry litter.

Immobilization of lead in shooting range soils by means of cement, quicklime, and phosphate amendments

Lead (Pb) contamination at shooting range sites is increasingly under environmental concern. Controlling Pb leachability from shooting range soil media is an important step to minimize Pb exposure to the surrounding environment. This study investigated stabilization of Pb in shooting range soils treated with cement, quicklime, and phosphate. Two soils were used and collected from two shooting ranges, referred to as SR1 and SR2. The treatment additives were applied to the soils at rates from 2.5% to 10% (w/w). The effectiveness of each treatment was evaluated by Pb (w/w). The effectiveness of each treatment was evaluated by Pb leachability, measured by the Toxicity Characteristic Leaching Procedure (TCLP). The possible mechanisms for Pb immobilization were elucidated using X-ray powder diffraction (XRPD). Cement and quicklime treatments were effective in immobilizing Pb in SR1 soil, with reduction of Pb concentration in TCLP leachate (TCLP-Pb) to be below the U.S. EPA non-hazardous regulatory limit of 5 mg L(-1) at application rates of > or =5% and 28-d incubation. By contrast, cement and quicklime amendments were less effective for Pb stabilization in SR2 soil because the TCLP-Pb levels in the treated soil were still higher than the limit of 5 mg L(-1) at all application rates, although they were significantly reduced in comparison with the untreated soil. Phosphate application was most effective in reducing Pb leach ing in both soils. Even at an application rate as low as 5% and 1-d incubation, phosphate could reduce TCLP-Pb to be below the limit of 5 mg L(-1) in both soils. Immobilization of Pb in the SR1 soil amended with cement and quicklime was attributed to the formation of pozzolanic minerals (e.g., calcium silicate hydrate C-S-H and ettringite) that could encapsulate soil Pb. The pozzolanic reaction was limited in the SR2 soil upon the application of cement and quicklime. Reduction of the TCLP-Pb might result from complexation of Pb on the surface of the formed calcite. Phosphate-induced Pb immobilization was mainly attributed to formation of less soluble PbHPO4. The results indicate that effectiveness of cementitious treatments (cement and quicklime) in immobilizing Pb varies in two soils, being effective in SR1 soil but less in SR2 soil. For one given soil, no difference was observed of the effeciveness between cement and quicklime treatments, whereas phosphate amendment emerges as a most effective treatment means for stabilizing Pb in both two soils, and it also shows a faster immobilization process and little effect on the soil acid buffering capacity. Recommendations and Perspectives. Overall, our study reveals that immobilizing Pb can be one of the best management practices for Pb contamination at shooting range sites. Phosphate amendment is most effective in immobilizing Pb in any kind of the soil ranges to minimize negative Pb impacts on the shooting range sites.

Chromium Leaching and Immobilization in Treated Soils

The purpose of this study is to investigate the effectiveness of a quicklime-based stabilization/solidification (s/s) technique to reduce the leachability of Cr(III) and Cr(VI) in laboratory-prepared soil. The soils were prepared by mixing kaolinite or montmorillonite with fine quartz sand and then subjecting the samples to s/s treatment. Treatment included quicklime, fly ash, and quicklime–fly ash additions. The effectiveness of the treatment was evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) test. To elucidate the controlling Cr(VI) immobilization mechanisms, slurry mixtures were prepared with potassium chromate (K2CrO4), quicklime, and fly ash. X-ray diffraction (XRD) analyses were performed to investigate the reaction products responsible for Cr(VI) immobilization. Experimental results indicate very low Cr(III) leachability upon quicklime treatment. All samples treated with quicklime and quicklime–fly ash show TCLP Cr(III) concentrations below the U.S. EPA TCLP limit of 5 ppm. However, neither quicklime nor fly ash treatment alone was effective in reducing Cr(VI) leachability. An effective reduction in Cr(VI) leachability was achieved only when both quicklime and fly ash were added to the laboratory-prepared soils. Previous research has attributed this reduction in Cr(VI) leachability to the fly ash-induced chemical reduction of Cr(VI) to Cr(III). However, in this study, fly ash was found to be an ineffective reducing agent. XRD analyses results for quicklime–fly ash slurries do not indicate the formation of CaCrO4 or CaCrO4 · 2H2O, which were identified in previous research as the reaction products responsible for Cr(VI) immobilization. A hypothesis is presented in this paper to explain these results and the effectiveness of quicklime-fly ash mixtures in reducing the leachability of Cr(VI). XRD analyses have also identified the pozzolanic compound 3CaOAl2O30.5CaCrO40.5CaSO4 · nH2O as the precipitate most likely responsible for Cr(VI) immobilization.

OPERATIONAL USE OF A MOBILE SAND-WASHING PLANT FOR CLEANING PEBBLES: THE AMAZZONE OIL SPILL

ABSTRACT On January 31, 1988, the Amazzone spilled about 1,500 tons of a highly paraffinic medium fuel oil (having a pour point of 36°C) along a distance of 300 km off the coast of Brittany. Due to very rough sea conditions, no offshore recovery operation could be carried out. Most of the pollution was beached as scattered patches on numerous sites, including pebble beaches in south Finistère, which had been especially difficult to clean during previous spills. In this area, the pebble banks that protect the dunes are relatively exposed to erosion. It was therefore decided to try cleaning these pebbles on site using the mobile plant that was designed for washing polluted sands and tested in 1985. The plant prototype was put in working order and conveyed to the site on the Baie d'Audierne. The equipment was very easily adapted to washing the pebbles polluted by a mixture of sand and fuel oil emulsion. A total of 1,400 m3 was cleaned during 10 days at the end of March. The plant worked smoothly with a load of 20 to 25 m3 of pebbles per hour and using a petroleum solvent as a washing agent. Because the ambient temperature was rather low (around 5°C), cleaning was performed with warmed water. Compared to other techniques that could be used to clean polluted pebble beaches, the washing plant proved very effective (providing good cleaning and high throughput) and competitive (costing less than quicklime treatment, for instance). Another advantage of this technique is that cleaned pebbles are returned to the beach, helping the pebble bank to keep its anti-erosion function.