Pilot-Scale Decontamination of Soil Polluted with As , Cr , 3 Cu , PCP , and PCDDF by Attrition and Alkaline Leaching

6 Abstract: Recently, an efficient and promising process was developed to allow the removal of As, Cr, Cu, pentachlorophenol (PCP), and 7 polychlorodibenzo-dioxins and furans (PCDDF) from soil using alkaline leaching. The present study evaluates the performance and the 8 robustness of this decontamination process for the treatment of four different polluted soils by attrition and alkaline leaching at a pilot scale. 9 The attrition process carried out on the coarse fraction (>0.125 mm) allowed the removal of 24–42% of As, 0–13% of Cr, 23–46% of Cu, 0– 10 85% of PCP, and 17–64% of PCDDF from the different contaminated soils. Removal yields of 87–95% of As, 50–72% of Cr, 73–84% of Cu, 11 52–100% of PCP, and 27–73% of PCDDF were obtained after three leaching steps (1⁄2NaOH 1⁄4 1 M; 1⁄2Cocamydopropylbetaine—BW 1⁄4 3% 12 (w/w); t 1⁄4 2 h; pulp density 1⁄2PD 1⁄4 10% [w/v]) conducted on the fine fraction (<0.125 mm). The performance of both attrition and alkaline 13 leaching processes seemed to be influenced by the nature of the soil and the type and initial level of contaminants present in the soils. 14 However, the entire leaching process seemed to be highly efficient, allowing the simultaneous reduction of concentrations of inorganic 15 and organic contaminants. The cost, including direct and indirect costs, were estimated between US$214 and 454 per ton of treated soil, 16 depending on the nature of the soil and the initial level of contamination. DOI: 10.1061/(ASCE)EE.1943-7870.0001255. © 2017 American 17 Society of Civil Engineers.

. In North America, numer-29 ous sites contaminated by both organic and inorganic compounds requiring remediation have been listed, including wood preservation industry sites.Since the 1970s, preservative agents have been applied to wood structures to protect them from insects and fungal attacks and enhance their service lifetime by 20-50 years (Janin 2009).Over the last few decades, the most commonly used wood preservative agents are chromated copper arsenate (CCA) and pentachlorophenol (PCP).The leaching of these preservative agents [As, Cr, Cu, PCP, and polychlorodibenzo-dioxins and furans (PCDDF)] from treated wood structures led to the contamination of soil by both organic and inorganic compounds.Indeed, some researchers highlighted that the inappropriate management and/ or storage of treated wood during the last few decades is responsible for the contamination of several sites across the world ( Usually, these soils are contaminated by metals (As, Cr, Cu) and organic compounds, such as PCP and PCDDF (Reynier 2012).
Currently, the only available options for the remediation of soils contaminated by both organic and inorganic compounds are limited to excavation, followed by thermal desorption to destroy organic contaminants, followed by the immobilization of inorganic contaminants or excavation, followed by disposal at off-site secured waste landfill sites (Dermont et al. 2008).However, these management options are becoming nonpreferable owing to the regulations regarding incineration and landfill leachate controls, which are becoming increasingly stringent (Reynier et al. 2013).In the last few years, various processes including thermal, biological, and physicochemical technologies have been the subject of several studies to allow the rehabilitation of soils contaminated by As, Cr, Cu, PCP, and PCDDF (Mouton et al. 2009).The thermal methods showed good results for PCP and PCDDF removal, but these technologies are inefficient for the removal of metals from contaminated soils (Lecomte 1998;Reynier 2012;Dufresne 2013).Kasai et al. (2004) showed that a thermal desorption method that 1 Ph.D. Student, Institut National de la Recherche Scientifique (Centre Eau, Terre et Environnement), Univ.du Québec, 490 Rue de la Couronne, QC, Canada G1K 9A9.E-mail: sabrine.metahni@ete.inrs.ca

Soil Sampling and Characterization
Four soil samples (D1, G2, S1, and S3) contaminated by As, Cr, Cu, PCP, and PCDDF were collected from different industrial areas.For each site, excavation of contaminated soils was performed using an excavator at a depth of 0-30 cm.More than  After the third attrition step, the soil samples were transferred in a 20-L plastic reactor and were then rinsed with 4 L of tap water using a Karcher electric sprayer (140 kg=cm 2 , Québec, QC, Canada) before being sieved.Approximately 2 L of tap water was sprayed on the different sieves (less than 0.125 mm for the 0.125-1 mm fraction, less than 0.5 mm for the 1-2 mm fraction, and less than 1 mm for the 2-4 mm fraction) to rinse each treated soil fraction.After the attrition process, each fraction of the different soils studied were dried at 60°C in a vacuum oven and analyzed to determine the residual concentrations of inorganic and organic contaminants.

Leaching Experiments
Leaching experiments were performed on the fine fraction (<0.125 mm) of the four different soils studied.The alkaline conditions of leaching (temperature, pH, PD, number of steps) were optimized in a previous study (Reynier 2012).The leaching process consisted of three leaching steps, 2 h each, followed by one rinsing step of 15 min.For all leaching assays, the PD was fixed at 10% (w/v) for the leaching steps and 28% (w/v) for the rinsing steps.(without any addition of acid or basis).To enhance the removal of organic contaminants, an amphoteric surfactant (BW) was added before each washing step, and its concentration was fixed at 3% (w/v).The leaching steps were conducted at 80 AE 7°C using a hotplate (Thermo Scientific Remote-Control Hotplates, Montreal, QC, Canada), whereas the rinsing steps were carried out at room temperature.During the leaching and rinsing steps, the mixing speed was fixed at 1,700 rpm using a mechanical stirrer (Light EV1 P25 AXFLOW, New York, NY).After each leaching and rinsing step, solid-to-liquid separation was carried out by removing most of the liquid using a lamella settler with a capacity of 20 L, a settling area of 0.44 m 2 , a length of 21 cm, and a height of 32 cm (Fiberglass, 14 lamella, Plastiver, Québec, QC, Canada).After the leaching and the rinsing steps, soil samples were collected and then dried at 60°C before being analyzed to determine the residual concentrations of PCP, PCDDF, and metals.

Alkaline Leachates Treatment by Precipitation
Leachate treatment was performed by precipitation-coagulation using 1 L of the effluent emerging from the first leaching step to concentrate the contaminants present in small amounts of sludge.
The precipitation-coagulation experiments were performed in

Results and Discussion
Soil Characteristics    Concerning the organic contaminants, the residual PCP and PCDDF concentrations measured in the coarse fraction ranged from 0.05 to 7.92 mg=kg and from 332 to 3,213 ng TEQ=kg, respectively.According to these results, the attrition process seemed to be more efficient for the removal of PCP and PCDDF from Soils S1 and S3, with removal yields ranging from 33 to 85% for PCP and 64% for PCDDF, than from Soils G2 and D1, with removal yields varying between 0 and 44% for PCP and between 17 and 36% for PCDDF.These results showed that the effect of attrition could be influenced by the nature of the soil and the type of contaminant.In the case of Soils G2 and D1, the performance of attrition to remove organic contaminants from the coarse particles might be improved by the use of an amphoteric surfactant, thus enhancing the solubilization of these hydrophobic organic contaminants.

Attrition Sludge Production
The attrition steps produced sludge that represented between 0.7 and 6.1% for the fraction 0.125-1 mm, between 8.1 and 31% for the fraction 1-4 mm, and between 8.0 and 20% for the fraction 4-12 mm of the total mass of the four different soils studied.Except for Soil S1, the amount of sludge produced during attrition increased as the size of the particles treated by attrition increased.
This effect can be a result of the more important disintegration of agglomerated particles from the coarser soil fraction during attrition.
Table 4 presents the amount of sludge produced during attrition treatment of the coarse fraction (>0.125 mm) and the inorganic and organic contaminant contents measured in the sludge.Depending on the soils treated by attrition, the total amount of sludge produced varied between 11.5 and 32.9% of all soil treated (coarse and fine fraction).The treatment by attrition of the coarse fraction, which represented between 80.8 and 96.3% of the soil, allowed the concentration of both inorganic and organic contaminants in small amounts of sludge, except for Cr.The attrition sludge can be disposed of in landfill sites or must be treated or disposed of in secured landfill sites, depending on the residual concentrations of contaminants and the regulations.
These results highlighted that attrition is an inexpensive and promising technique to simultaneously remove inorganic and organic contaminants from the coarse particles of soil and concentrate 403 them into small amounts of sludge, even if its performance seemed 404 to vary, depending on the nature of both soil and contaminant and 405 the initial levels of organic and inorganic contaminants.and >81% for PCDDF).The differences observed could be explained by the fact that it is more difficult in the present study to efficiently remove organic contaminants from the fine fraction owing to their very high initial contents of PCP and PCDDF.
According to results of the present study, the performance of the leaching process in the removal of organic contaminants might be influenced by the nature of the soil and/or the type of contaminants.
Indeed, the performance of the leaching process seemed to be more variable for the removal of PCP and PCDDF from soil than for As, Cr, and Cu.However, these results highlighted that the use of NaOH in combination with an amphoteric surfactant BW is efficient to simultaneously reduce the concentration of As, Cr, Cu, PCP, and PCDDF from soils with different levels of contamination.

Production
The primary disadvantage of using chemical processes to remove contaminants from soils is the production of large amounts of alkaline leachates that should be treated to concentrate the contaminants into small amounts of sludge.Table 6 soil contaminated by organic and/or in-22 organic compounds have become a major concern, affecting human 23 health and causing a serious threat to the environment (Napola et al. 24 2006; Mouton et al. 2009).The primary reasons for soil contami-25 nation are improper industrial discharge, inappropriate disposal 26 of wastes, mine tailings, the use of pesticides, combustion and the 27 industry of wood preservation, and certain natural resources 28 Cooper and Ung 1997; Stefanovic and Cooper 2005; Hasan et al. 2010).

[
98.9% removal of PCDDF in a laboratory-scale 64 experiment could be efficiently used for the remediation of conta-65 minated soil.Bioremediation methods usually referred to the use 66 of microorganisms such as fungi and bacteria to break down com-67 plex organic contaminants into simpler compounds such as CO 2 , 68 H 2 O, CH 4 , and chlorine (Doyle 2008).However, these methods 69 required long periods to remove or degrade organic contaminants, 70 ranging from a few weeks to a few months, and their applicability 71 to soils contaminated by metals and PCDDF is restricted (Lecomte 72 1998).Soil washing is another method of treatment that can be used 73 to remediate both organic and inorganic contaminants using 74 physicochemical treatment methods.Chemical extraction can 75 be achieved using different reagents including inorganic (sulfuric, 76 nitric, phosphoric acids) or organic acids (acetic, citric acid) 77 (Subramanian et al. 2010; Lafond et al. 2012), chelating agents 78 [ethylenediaminetetraacetic acid (EDTA), ethylenediamine disuc-79 cinic acid (EDSS)] (Rivero-Huguet and Marshall Tween 80 (TW), cocamidopropylhydroxysultaine (CAS), cocami-82 dopropylbetaine (BW), Brij 35, and Brij 98] (Mouton et al. 2009; 83 Rivero-Huguet and Marshall 2011; Reynier 2012; Torres et al. 84 2012).Physical separation may be performed alone or in combi-85 nation with chemical treatments to enhance the performance of 86 contaminant removal from coarse soil fraction while reducing the 87 operational costs.Physical separation methods such as mechanical 88 screening, froth flotation, magnetic separation, attrition scrubbing 89 and hydrodynamic classification can be efficiently used to remove 90 metals from soil and concentrate these contaminants into small 91 quantities of soil, especially for the rehabilitation of sites with large 92 amounts of contaminated soil owing to the low operational costs of 93 these technologies (Dermont et al. 2008).The most common physi-94 cal separation method used for the decontamination of coarse 95 particles of soil contaminated by both organic and inorganic com-96 pounds is attrition (Taillard 2010; Bisone 2012).Indeed, mechani-97 cal rotation used during the attrition processes caused collision 98 between large particles that released the contaminants and concen-99 trated them into the fine fraction (Bergeron et al. 1999).An efficient 100 leaching process using flotation in acidic media (sulfuric acid) in 101 the presence of an amphoteric surfactant (BW) was identified to 102 remove organic compounds and metals from soil contaminated

Fig. 1
Fig. 1 shows a diagram of the entire process used for the decontamination of the four soils contaminated by As, Cr, Cu, PCP, and PCDDF.Attrition experiments were applied to the coarse fractions (4-12, 1-4, and 0.125-1 mm) of four different soil samples, which represented between 87 and 95% (w/w) of the total soil.Soil particles larger than 12 mm were not treated by attrition because of the low levels of inorganic (As, Cr, Cu) and organic (PCP, PCDDF) contaminations.The attrition process consisted of three 20-min attrition steps performed in a 10-L capacity stainless steel reactor equipped with three deflectors and a mechanical stirrer (Light EV1 P25 AXFLOW, New York).The mixing speed was fixed at 1,700 rpm.Attrition experiments were carried out onto 2 kg of soil sample mixed with tap water (pH around 7) to obtain a 40% PD (w/w).After each 20-min attrition step, treated soils were separated from the water using 2, 0.5, and 0.125 mm sieves for the 4-12, 1-4, and 0.125-1 mm soil fractions, respectively.The treated soil was then washed with 4 L of tap water before being reintroduced to the attrition process to undergo the next attrition step.

Y
Leaching experiments were performed in a 25-L capacity stainless steel reactor by mixing 2 kg of soil with 18 L of alkaline solution (1 M NaOH, Laboratories MAT, Quebec, Canada).The initial pH value of the pulp was around 13-13.5 all along the experiments

Imhoff 9 cones[ 9 . 1 Fig. 1 .
. A solution of sulfuric acid (93% H 2 SO 4 ) was used to reduce the pH of the leaching solution from 13.0-13.5 to 211 7.5-8.0.Between 2.95 and 4.30 g=L of a solution of ferric sulfate 212 65% of iron (w/w), Chemco, Saint-Augustin-de-Desmaures, 213 QC, Canada] was added to the solution under agitation to improve 214 the removal of As.Indeed, some research showed that the addition 215 of ferric ions during the precipitation allowed the formation of a 216 precipitate of iron arsenate (FeAsO 4 • 2H 2 O) and the adsorption 217 of As ions onto ferric hydroxide molecules, thus improving the re-218 moval of As from effluents (Coudert et al. 2014).The addition of 219 ferric sulfate led to an acidification of the solution that depended on 220 the amount added.To avoid any resolubilization of As, Cr, Cu, and 221 PCP resulting from the acidification observed, a solution of sodium 222 hydroxide [ðNaOHÞ ¼ 0.5 M] was then added to adjust the final 223 pH of the solution between 7.0 and 7.3.The solution was then left 224 to settle overnight, and the sludge produced was then collected and 225 dried at 60°C.The concentrations of inorganic and organic contam-226 inants were determined in the different sludge samples collected.the soil before and after treatment were deter-230 mined in the laboratories at the National Institute of Scientific Re-231 search (INRS) by inductively plasma coupled to atomic emission 232 spectroscopy (ICP-AES) (Vista Ax CCO simultaneous ICP-AES, 233 Varian, Mississauga, ON, Canada) after digestion of 0.5 g of dry 234 soil samples in the presence of nitric and hydrochloric acids (HNO 3 235 and HCl) according to Method 3030I (APHA 1999).Each soil sam-236 ple was digested and analyzed in triplicate.During each series of F1:Diagram of the treatment process applied for the rehabilitation of four different soils contaminated by As, Cr, Cu, PCP, and PCDDF blanks, reference certified soil samples [CNS 238 392-050, PQ-1, lot No. 7110C513, CANMET, Canadian Certified 239 Reference Materials Project (CCRMP)], and certified standard so-240 lutions (Multi-elements standard, Catalog No. C00-061-403, SCP 241 Science, Lasalle, QC, Canada) were analyzed to ensure the quality 242 of the analysis.243 Organic Contaminant Analysis 244 PCP contents in the soil before and after treatment were determined in 245 the laboratories 10 according to the Centre d'expertise en analyse envi-246 ronnementale du Québec (CEAEQ) method (CEAEQ 2013) after the 247 solubilization of PCP from 20 g of soil by Soxhlet extraction in the 248 presence of methylene chloride (300 mL).PCP was then transferred 249 to an aqueous phase (solution of sodium hydroxide at 20 g=L) by 250 liquid/liquid extraction to perform a derivatization step in the presence 251 of anhydrous acetate and a solution of potassium carbonate (75%, v/ 252 v).After 12 h, a liquid/liquid extraction step was carried out using 253 methylene chloride.A solution of phenanthren-d 10 (internal standard) 254 was added, and then PCP analysis was performed by gas chromatog-255 raphy with mass spectroscopy (GC-MS) (Perkin Elmer, model 256 Clarus 500, column type Rxi-17, 30 m × 0.25 mm × 0.25 μm).257 The analysis of the 17 toxic congeners of PCDDF was per-258 formed according to the CEAEQ method MA. 400-D.F.1.1 259 (CEAEQ 2011) by an external laboratory (Wellington Laboratories, 260 Guelph, ON, Canada).261pH Measurements 262 The pH was determined using a pH-meter (Accumet Model 11 915) 263 equipped with a double junction Cole-Parmer electrode with an Ag/ 264 AgCl reference cell.Before each series of measurements, certified 265 buffer solutions (pH ¼ 2, 4, 7, and 10) were used to calibrate the 266 pH-meter.The total solid contents were measured according to the 267 APHA method 2540D (APHA 1999).268 Economic Analysis 269 The direct and indirect costs related to the treatment of the four 270 different soils contaminated by As, Cr, Cu, PCP, and PCDDF by attrition (>0.125 mm soil fraction) and alkaline leaching (<0.125 mm) were estimated for a decontamination plant able to treat 15,000 t of soil per year (operating period: 350 d=year; treatment capacity: 48 t=d; operating efficiency factor: 90%).The decontamination process plant was designed in countercurrent mode, which means that the effluents produced were recycled into the decontamination process to reduce the consumption of chemicals and water.In the economic analysis, the operating cost included the costs related to the use of chemical products such as H 2 SO 4 [US$80=t for a solution at 93% (w/w)], BW (US$1=kg), Fe 2 ðSO 4 Þ 3 (US$200=t), and NaOH (US$500=t); the consumption of electricity (US$0.07=kWh),water (US$0.50=m 3 ), and fuel (US$3.50=t);and the labor (US$25=h).The costs related to the transport and disposal of contaminated soils (US$120=t), highly contaminated soils (US$500=t for the transport, thermal destruction, and landfilling), and inorganic and organic hazardous wastes including sludge coming from the precipitation-coagulation (US$500=t) were also included in the estimation of the direct costs.The indirect costs included the administrative staff, insurance and taxes, research and development, and capital costs.The capital costs were evaluated using a 10-year reimbursement period for all equipment required for the treatment of soils by attrition and leaching and for the treatment of leachates by precipitation with a 5% annual interest rate.

30988. 1
to 283 mg Cu=kg, and from 0.66 to 29.3 mg PCP=kg.The dis-310 tribution of the contaminants in the four different soils studied 311 showed that the finer fraction (<0.125 mm) was most contaminated 312 than the coarser fraction (>0.125 mm).According to Anderson 313 et al. (1999), the increase of surface area, cationic exchange poten-314 tial in the fine fraction, and the innate shape of silts and clays 315 are important parameters favoring the attraction of contaminants 316 to the fine fractions of soils.Dermont et al. (2008) also reported 317 that the contaminants are generally associated with fine particles 318 (clay and silt), which are more potentially reactive as they have 319 a higher surface area than coarser particles.factors and the associated toxic 321 equivalent quantity (TEQ) values for each dioxin and furan conge-322 ner present in the coarse fraction (>0.125 mm) and the fine fraction 323 (<0.125 mm) of the four different soils.These results showed that 324 the 17 congeners known to be toxic were present in the coarse and 325 fine fractions of all soils.According to these results, the fixation of 326 PCDDF seemed to more important and favorable on the finer frac-327 tion for the different soils; the concentrations of PCDDF were 5-328 22 times higher in the fine fraction (2,990-45,770 ng TEQ=kg) 329 than in the coarse fraction (520-1,340 ng TEQ=kg).A comparison 330 of the concentrations of dioxin and furans substituted at the same 331 position showed that the concentrations of dioxin compounds 332 seemed to be higher than those of furan compounds in the different 333 soil fractions and for all of the soils studied.334 Efficiencies of Attrition Treatment on the Coarse 335 Fraction (>0.125 mm) 336 Three attrition steps 20 min each, carried out at room temperature 337 with a pulp density fixed at 40% (w/w), were applied to the coarse 338 fraction (4-12, 1-4, and 0.125-1 mm) of the different soils studied.the concentrations of As, Cr, Cu, PCP, and PCDDF 342 measured in the recombined soil fraction (>0.125 mm) before 343 and after treatment by attrition and the associated removal yields.344After the treatment by attrition, the residual concentrations of in-345 organic contaminants in the coarse fraction (>0.125 mm recom-346 bined soil fraction) ranged from 19 to 37 mg As=kg, from 22 to 347 195 mg Cr=kg, and from 41 to 67 mg Cu=kg.The entire attrition 348 process allowed the removal of 24-42% of As, 0-13% of Cr, and 349 23-46% of Cu.According to a study by Williford et al. (1999), a 350 pretreatment by attrition allowed similar removal yields (26.8% for 351 Cr) to those observed in the present study.The low efficiencies of 352 As, Cr, and Cu removal observed during the attrition process can be fact that the solubilization of these metals is unfavorable at pH ¼ 7, and only a small proportion of the inorganic contaminants is fixed to the fine particles agglomerated to the coarse particles and dislodged by attrition.Usually, attrition is used as a pretreatment to enhance the performance of inorganic contaminant removal by gravimetric separation technologies and not as a treatment itself.However, the attrition process developed seemed to be efficient enough to remove As, Cr, and Cu from the coarse fractions and allow the potential reutilization of the treated soils, depending on the current national regulations.
2 h each were applied to the fine soil fraction 409 (<0.125 mm) of four different soils at 80 AE 7°C to evaluate the 410 removal efficiencies of both organic and inorganic contaminants.411 The pulp density was fixed at 10% (w/w), and the leaching solution 412 was composed of NaOH (1 M) and an amphoteric surfac-413 tant ½ðBWÞ ¼ 3% ðw=wÞ.414 Performance of the Leaching Process on Inorganic and 415 Organic Contaminant Removal 416 Table 5 shows the contents of As, Cr, Cu, PCP, and PCDDF mea-417 sured in the fine soil fraction (<0.125 mm) before and after treat-418 ment by alkaline leaching and the associated removal yields.These 419 results highlight the necessity to develop an efficient method of 420 decontamination to allow the simultaneous removal of both organic 421 (PCP and PCDDF) and inorganic (As and Cu) contaminants.422 After three alkaline leaching steps, the residual concentrations 423 of inorganic contaminants in the fine fraction (<0.125 mm) ranged 424 from 30.0 to 99 mg As=kg, from 141 to 286 mg Cr=kg, and from 425 129 to 234 mg Cu=kg.These results show that the entire leaching 426 process was quite effective in solubilizing inorganic contaminants, 427 especially As and Cu, with removal yields ranging from 87 to 95% 428 for As and from 73 to 84% for Cu, whereas it seemed to be rel-429 atively less effective in the removal of Cr (from 50 to 72% of 430 Cr removed) from the different soils studied.These removal yields 431 were slightly higher than those observed by Reynier et al. (2014) 432 after three 2-h leaching steps carried out at 80°C in the presence of 433 NaOH (0.75 M) and BW [3% (w/w)] with a PD fixed at 10% (w/w).434 Indeed, these authors 13 obtained removal yields between 70 and 89% 435 for As, between 23 and 66% for Cr, between 59 and 71% for Cu, 436 and between 77 and 90% for PCP.The difference observed can be 437 attributed to the fact that the concentration of NaOH used in the 438 present study was fixed at 1 M, thus increasing the solubilization 439 of metals under anionic forms.According to Reynier et al. (2015), 440 As was mainly solubilized as AsO 3− 4 and HAsO 2− 4 (<1%) during presents the amount of sludge produced during the treatment of alkaline leachates by precipitation-coagulation and the inorganic and organic contaminant contents measured in the sludge.Depending on the fine soil fraction treated by leaching, the total amount of sludge produced during the treatment of leachates by precipitation-coagulation varied between 1.1 and 3.7% (w/w) of all soil treated.The treatment by precipitation-coagulation of alkaline leachates concentrated the inorganic and organic contaminants, especially PCDDF, in small amounts of sludge, thus reducing the costs related to waste disposal.Indeed, the treatment of leachates by precipitation-coagulation at pH ¼ 7 in the presence of ferric ions allowed the precipitation of metals as CrðOHÞ 3 , CuðOHÞ 2 , Cu 3 ðAsO 4 Þ:2H 2 O or FeAs2H 2 O 14 or the adsorption of metals onto ferric hydroxides or oxy-hydroxides (Reynier et al. 2015).Moreover, the precipitation of ferric hydroxides or oxy-hydroxides enhances the removal of hydrophobic organic contaminants such 491 as PCP and PCDDF, allowing their adsorption by electrostatic in-492 teractions (van der Waals interactions) on the flocs produced.493 The contaminant contents measured in the sludge produced 494 during precipitation-coagulation varied between 975 and 495 2,550 mg As=kg (dry basis), between 930 and 1,500 mg Cr=kg, 496 between 1,690 and 2,820 mg Cu=kg, between 11.1 and 497 699 mg PCP=kg, and between 23,400 and 128,000 ng TEQ=kg, de-498 pending on the initial level of contamination present in the fine soil 499 fraction (<0.125 mm).Owing to the large amounts of both organic 500 and inorganic contaminants measured in sludge, these residues 501 should be properly and safely managed according to the regulations 502 established in the country.the cost related to the treatment of different soils 505 contaminated by As, Cr, Cu, PCP, and PCDDF by attrition 506 (>0.125 mm soil fraction) and alkaline leaching (<0.125 mm soil 507 fraction) (Scenario 1), whereas Table 8 presents the cost related to 508 the treatment of the coarse fraction by attrition and the landfilling of 509 the fine fraction (Scenario 2).The total cost, expressed in US$=t, 510 include the direct, indirect, and capital costs estimated for the 511 decontamination of 15,000 t of contaminated soils per year.512 The global cost related to the decontamination of different soils 513 contaminated by As, Cr, Cu, PCP, and PCDDF ranged from 514 US$353 to US$521=t for Scenario 1 and from US$235 to 515 US$443=t for Scenario 2. As expected, the main parameters 516 impacting the decontamination cost are the performance of both 517 the attrition and alkaline leaching processes and the ultimate 518 amounts of heavily contaminated soil and hazardous wastes (met-519 allic sludge) to be appropriately disposed of.Indeed, if the attrition 520 or alkaline leaching processes did not sufficiently reduce both 521 organic and inorganic contaminants, the soil fraction should be number '2' has been inserted in this reference.Please check and confirm the edit made here.27. Please provide issue number for Torres et al. (2012).

Table 1
presents the concentration of As, Cr, Cu, PCP measured in each soil fraction (>12, 4-12, 1-4, 0.125-1, and <0.125 mm) of the four different soils studied and the soil fraction proportion.According to the particle-size distribution of the different soils, the coarse particles (>0.125 mm) represented the majority of the soils with proportions ranging from 80.8 to 96.3%, whereas fine particles (<0.125 mm) represented only between 3.7 and 19.2% of

Table 1 .
Concentrations of Contaminants Measured in the Different Soil Fractions from Four Different Soils Studied 304all soils.For soil samples G2, S1, and S3, the texture class of the 305 entire soil is silty sand, whereas the texture class of D1 is sand.306 The concentrations of As, Cr, Cu, and PCP measured in all soil 307 samples were very different among the four soils studied, ranging 308 from 57.7 to 201 mg As=kg, from 65.2 to 164 mg Cr=kg, from

Table 2 .
Concentrations of Each Dioxin and Furan Measured in the Different Soil Fractions from Four Different Soils Studied a From OTAN and CDSM (1988).

Table 4 .
Sludge Production and Contaminant Concentrations Measured in the Sludge Produced during the Treatment of the 0.125-12 mm or 0.125-25 mm Soil Fractions by Attrition

Table 5 .
Concentrations of Contaminants Measured in the Soil Fraction <0.125 mm before and after Leaching Treatment

Table 6 .
Concentration of Inorganic and Organic Contaminants in the Sludge Obtained after Treatment of the Leachate by Precipitation-

Table 7 .
Direct and Indirect Costs Related to the Treatment by Attrition (>0.125 mm) and Alkaline Leaching (<0.125 mm) of Different Soils Contaminated by As, Cr, Cu, PCP, and PCDDF

Table 9 .
Determination of the Direct and Indirect Costs Related to the Decontamination of Different Soils Contaminated by As, Cr, Cu, PCP, and PCDDF Depending on the Treatment Plant Capacity