environmental risk assessment and stabilization/solidification of zinc extraction residue: ii....

Hydrometallurgy 105 (2011) 270–276

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Environmental risk assessment and stabilization/solidification of zinc extractionresidue: II. Stabilization/solidification

Mehmet Erdem ⁎, Arzu ÖzverdiDepartment of Environmental Engineering, Fırat University, 23279 Elazığ, Turkey

⁎ Corresponding author. Tel.: +90 424 2370000; fax:E-mail address: [email protected] (M. Erdem).

0304-386X/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.hydromet.2010.10.014

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a r t i c l e i n f o
Article history:Received 4 September 2010Received in revised form 22 October 2010Accepted 24 October 2010Available online 2 November 2010

Keywords:Metallurgical wasteHeavy metal pollutionZincSolidification and stabilizationTCLP

Heavy metal contamination is an important problem that is encountered at many metallurgical sites.Solidification/stabilization is a widely applied remediation technology for heavy metal contamination. In thestudy, solidification and stabilization of zinc extraction residue containing some heavy metals (e.g. Pb, Zn, Cd,Mn) which can leach using Portland cement, fly ash and lime was examined. Zinc extraction residue wassolidified and stabilized with different amounts of Portland cement, fly ash and lime for heavy metalimmobilization. Leaching behavior of all solidified/stabilized products was tested by pH dependent batchleaching test, Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation LeachingProcedure (SPLP). The results were evaluated in order to determine if the solidified/stabilized products can bedisposed of at a landfill site with domestic waste or at a segregated landfill. Mechanical strength decreaseswith increase in the waste content. Heavy metals in the waste could be considerably immobilized by thesolidification/stabilization process.

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1. Introduction

Zinc is one of the most important metals. It is generally producedfrom its sulphide, carbonate, oxide ores or electric arc furnace dusts,some metallurgical ash and residues by hydrometallurgical, pyromet-allurgical or their combination processes. Hydrometallurgical processesare favorable for ZnO-rich materials, while pyrometallurgical andcombination processes are preferred for sulphide or carbonate-baseraw materials.

In the hydrometallurgical zinc production processes, Zn is firstleached with sulphuric acid solution and then pregnant Zn solutionand solid extraction residue containing unextractable Zn and someheavy metal compounds such as Pb, Cd and Mn are obtained afterliquid-solid separation by rotary filter. Pregnant Zn solution is purifiedand Zn is won by electrolysis, while solid extraction residue of theprocess is generally stockpiled. In the big hydrometallurgical zincproduction plants, about 100 metric tons of zinc extraction residuescan be generated daily. These residues are considered as hazardouswaste due to their soluble heavy metal content (Altundoğan et al.,1998; Özverdi and Erdem, 2010). In our previous study, we havedetermined that the concentrations of themetal leached from the zincextraction residue exceeded the US EPA's toxicity characteristicthreshold for Pb (5 mg/l) and Cd (1 mg/l) (Özverdi and Erdem,

2010). Due to heavy metal contamination, this waste cannot bedisposed of at landfills without treatment.

Among the management ways of heavy metal containing waste,solidification/stabilization (S/S) is known as an effective remediationmethod prior to disposal. S/S technologies are widely applied fortreatment of hazardous wastes such as sludges, slags and ashescontaining heavy metals. Main purposes in the S/S processes are toreduce the hazard of a waste by converting the contaminants into lesssoluble, mobile or toxic forms and to encapsulate the waste in amonolithic solid of high structural integrity by using some additivessuch as metal stabilization additives and binding materials (Connerand Hoeffner, 1998). S/S processes not only improves the physical andchemical properties of the wastes, but also cheap due to using ofcheapest binders such as cement, lime, pozzolan when it is comparedto other treatment techniques. S/S processes have been applied to alot of industrial wastes containing heavy metal such as blasted copperslag (Zain et al., 2004), galvanic sludge (Luz et al., 2006), electric arcfurnace dusts (Pereira et al., 2001; Pelino et al., 2002; Salihoglu et al.,2007; Bulut et al., 2009), heavy metal sludges (Andrés et al., 1998;Diet et al., 1998; Qian et al., 2006) and foundry sludge (Ruiz andIrabien, 2004).

Zinc extraction residues contain mainly of zinc, lead, cadmium andiron. Since the concentrations of lead and cadmium leached from theresidue exceed the US EPA's toxicity characteristic threshold for Pb(5 mg/l) and Cd (1 mg/l) (TCLP), it has been determined that the leadand cadmium are the greatest potential risk (Özverdi and Erdem,2010). Thus, immobilization of the lead and cadmium in this waste isvery important for a waste management perspective. A lot of studies

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Table 1The samples prepared in solidification/stabilization experiments and their chemicalcompositions.

Composition ofsolidified/stabilizedspecimen

Constituents

Pb, % Zn, % Fe, % Al, % Si, % Cd,mg/kg

1 PC 10%+ZER 90% 12.47 7.69 6.41 4.03 14.30 2222 PC 20%+ZER 80% 10.26 5.85 5.33 3.82 13.51 2013 PC 30%+ZER 70% 9.61 4.48 4.76 3.46 12.62 1754 PC 40%+ZER 60% 7.93 4.26 4.08 3.41 12.14 1395 PC 50%+ZER 50% 6.72 4.11 3.71 3.29 11.63 1216 FA 10%+ZER 90% 12.18 7.92 5.96 4.32 14.70 2177 FA 20%+ZER 80% 10.42 6.09 5.57 4.13 14.35 2028 FA 30%+ZER 70% 8.63 5.44 5.33 4.52 14.21 1499 FA 40%+ZER 60% 7.54 4.82 5.27 4.74 14.46 13010 FA 50%+ZER 50% 6.46 4.29 4.73 4.98 13.66 10311 PC 90%+FA 10%+

ZER 50%+Sand 50%3.86 2.05 4.61 4.52 15.96 97

12 PC 80%+FA 20%+ 3.73 2.54 4.54 4.56 16.09 96

271M. Erdem, A. Özverdi / Hydrometallurgy 105 (2011) 270–276

have been performed to investigate the immobilization of lead in solidwastes and contaminated soils. In these studies, phosphate (Melamedet al., 2003; Cao et al., 2003; Chen et al., 2003; Geysen et al., 2004a,b;Liu and Zhao, 2007; Matusik et al., 2008; Song et al., 2009) andhydroxiapatite (Xu and Schwartz, 1994; Sugiyama et al., 2002;Mavropoulos et al., 2004; Cao et al., 2009) have been generally usedas an immobilization reagent. It has been reported that the P additionin wastes/soils containing lead can effectively transform various Pbminerals into insoluble chloropyromorphite (Cao et al., 2008). Fly ash,red mud (Ciccu et al., 2003; Bertocchi et al., 2006; Çoruh and Ergun,2010) and bauxite (Ciccu et al., 2003) have also been tested for heavymetal immobilization.

The main purpose of this study was to investigate S/S of the zincextraction residue by using Portland cement, fly ash and lime and todecide whether the products solidified/stabilized could be landfilledor disposed of at a segregated site by pH dependent batch leachingtest, TCLP and SPLP tests.

ZER 50%+Sand 50%13 PC 70%+FA 30%+

ZER 50%+Sand 50%3.76 2.16 4.73 4.91 16.36 92

14 PC 60%+FA 40%+ZER 50%+Sand 50%

3.70 2.22 4.92 4.95 16.66 89

15 L 10%+ZER 90% 11.62 7.56 5.29 3.69 13.57 22616 L 20%+ZER 80% 10.04 5.27 4.68 3.27 12.06 19317 L 30%+ZER 70% 8.21 4.31 3.86 2.44 9.11 17418 L 40%+ZER 60% 7.94 3.83 3.54 2.05 7.36 15219 L 50%+ZER 50% 6.74 3.46 3.23 1.88 4.81 10520 PC 90%+L 10%+

ZER 50%+Sand 50%3.69 2.11 4.64 4.32 16.31 90

21 PC 80%+L 20%+ZER 50%+Sand 50%

3.71 2.04 4.61 4.38 15.94 92

22 PC 70%+L 30%+ZER 50%+Sand 50%

3.74 2.08 4.60 4.29 16.09 92

23 PC 60%+L 40%+ZER 50%+Sand 50%

3.52 2.04 4.58 4.33 15.76 92

2. Materials and methods

2.1. Materials

As described in previous paper of this research, the ZER used in thisstudy was obtained from a zinc plant located in Kayseri, Turkiye. Itwas dried at room temperature for 10 days prior to use and thenstored in a tightly closed jar throughout the study. Details of thechemical analysis andmineralogical composition of the ZER have beengiven in the previous paper (Özverdi and Erdem, 2010).

Ordinary Portland cement (PC), fly ash (FA) and lime (L) wereused as S/S reagents. PC (PC 42.5 type) and FA were obtained fromAltinova Cement Factory in Elaziğ and Afşin-Elbistan Thermal PowerPlant, Kahramanmaraş, Turkiye, respectively. All samples were driedat 50 °C for 4 h and then sieved to obtain particles smaller than 149micron (−100 mesh).

For the preparation of reference solutions, Merck standards foratomic absorption spectrometry were used. All working solutionswere prepared with distilled water and analytical grade reagents.

2.2. Experimental

2.2.1. Solidification/stabilization experimentsS/S of ZER was carried out by makingmortar samples with ZER, PC,

FA, L, sand and deionised water. For this purpose, twenty-threemortars having different compositions given in Table 1 wereprepared. FA and L were used as cement replacement in the mortarmixes. Due to nonpuzzolonic character of the ZER, sand was addedinto some mortars to obtain a monolithic solid of high structuralintegrity with binders. The ZER and binding materials (PC, FA and L)were mixed requisite amount of deionised water (water/binder ratio0.6) using a mixer. Amount of the water used does not cause ooze andcan turn the mixture into mud. The mortars were then poured intomoulds size of 10 cm×10 cm×10 cm. The compacted samples werehardened and then air cured for 28 days to prevent loss of heavymetalions. After 28 days, compressive strengths of the cubic S/S productscement-based were tested using a hydraulic type Bescom testingmachine. The samples crushed were sieved and then subjected to theleaching experiments.

2.2.2. Leaching testsLeaching behavior and pollution potential of the solidified and

stabilized samples were evaluated by batch leaching tests, toxicitycharacteristic leaching procedure (TCLP) (USEPA, 1990) and syntheticprecipitation leaching procedure (SPLP) (USEPA, 1994) details ofwhich described in the previous paper (Özverdi and Erdem, 2010).

All leaching experiments were performed in duplicate and meanvalues were taken into account. The values obtained in duplicateswere found to vary within ±5%.

2.2.3. Methods of analysisPhilips PW-2404 electron X-ray fluorescence spectroscopy and

Shimadzu XRD-6000 X-ray diffractometer were used for determina-tion of chemical and mineralogical compositions of the samples,respectively. Perkin Elmer AAnalyst 800 was used to determine themetal ion concentrations released from the samples in to the testsolutions.

3. Results and discussions

3.1. Chemical and mineralogical compositions of S/S products

Chemical and mineralogical characterization is the first step in theexamination of leaching behavior of wastes. Particularly, in order toclarify S/S mechanism, type and concentration level of the pollutantsin the waste and crystal shape of their compounds are important.Therefore, all samples prepared were subjected to chemical andmineralogical analysis. The results have been given in Tables 1 and 2.

As seen from Table 1, Pb and Zn content of the samples solidified/stabilized depending on amount of the additives vary in the range of3.52–12.47% and 2.04–7.92%, respectively.

It has been determined that the Pb in the form of anglesite which isthe main contaminant in the ZER was transformed into susannite[Pb4SO4(CO3)2(OH)2] and cerrusite [PbCO3] minerals by S/S treat-ments (Table 2).

Table 2Mineralogical compositions of the solidified/stabilized samples.

S/S product Mineralogy Chemical formula

PC 10%+ZER 90% Gypsum CaSO4.2H2OQuartz SiO2

Maghemite Fe2O3

Anglesite PbSO4

Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2OSusannite (minor) Pb4SO4(CO3)2(OH)2Cerrusite (minor) PbCO3

Clorite (minor) A5-6T40Z8-10A:Al, Fe2+, Fe3+,Mn, Mg, Li, or Ni.T:Al, Fe3+, Si or theircombinationZ: O or OH.


Maghemite Fe2O3

Anglesite PbSO4


Clorite (minor) A5-6T40Z8-10 A:Al, Fe2+,Fe3+, Mn, Mg, Li, or Ni.T:Al, Fe3+, Si or theircombinationZ: O or OH.


Maghemitee Fe2O3

Anglesite (minor) PbSO4


Clorite (minor) A5-6T40Z8-10 A:Al, Fe2+,Fe3+, Mn, Mg, Li, or Ni.T:Al, Fe3+, Si or theircombinationZ: O or OH.

PC 40%+ZER 60% Gypsum CaSO4.2H2OLarnite Ca2SiO4

Quartz SiO2

Maghemite Fe2O3


Ettringit (minor) Ca6Al2(SO4)3(OH)12.26H2OSusannite (minor) Pb4SO4(CO3)2(OH)2Cerrusite (minor) PbCO3

PC 50%+ZER 50% Gypsum CaSO4.2H2OLarnite Ca2SiO4

Portlandite Ca(OH)2Maghemite Fe2O3

Susannite Pb4SO4(CO3)2(OH)2Anglesite (minor) PbSO4

Quartz (minor) SiO2

Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2OFA 10%+ZER 90% Gypsum CaSO4.2H2O

Portlandite Ca(OH)2Susannite Pb4SO4(CO3)2(OH)2Quartz (minor) SiO2


Maghemite (minor) Fe2O3

Cerrusite (minor) PbCO3

Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2OFA 20%+ZER 80% Gypsum CaSO4.2H2O



Susannite Pb4SO4(CO3)2(OH)2Portlandite (minor) Ca(OH)2Quartz (minor) SiO2

FA 30%+ZER 70% Gypsum CaSO4.2H2OPortlandite Ca(OH)2Susannite Pb4SO4(CO3)2(OH)2Quartz (minor) SiO2




Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2O

Table 2 (continued)


FA 40%+ZER 60% Gypsum CaSO4.2H2OQuartz SiO2

Susannite (minor) Pb4SO4(CO3)2(OH)2Anglesite (minor) PbSO4

Maghemite (az) Fe2O3

Cerrusite PbCO3

Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2OFA 50%+ZER 50% Quartz SiO2

Gypsum CaSO4.2H2OSusannite Pb4SO4(CO3)2(OH)2Anglesite (minor) PbSO4

Maghemite Fe2O3

Cerrusitee (minor) PbCO3

Ettringite Ca6Al2(SO4)3(OH)12.26H2OPC 90%+FA 10%+ZER 50%+Sand 50%

Quartz SiO2

Calcite CaCO3

Ettringit (minor) Ca6Al2(SO4)3(OH)12.26H2OGypsum (minor) CaSO4.2H2OSusannite (minor) Pb4SO4(CO3)2(OH)2Larnite Ca2SiO4

Clorite A5-6T40Z8-10A:Al, Fe2+, Fe3+,Mn, Mg, Li, or Ni.T:Al, Fe3+, Si orcombinationsZ: O or OH.

PC 80%+FA 20%+ZER 50%+Sand 50%

Quartz SiO2

Calcite CaCO3

Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2OGypsum (minor) CaSO4.2H2OSusannite (minor) Pb4SO4(CO3)2(OH)2Larnite Ca2SiO4

Clorite A5-6T40Z8-10 A:Al, Fe2+,Fe3+, Mn, Mg, Li, or Ni.T:Al, Fe3+, Si or theircombinationZ: O or OH.

PC 70%+FA 30%+ZER 50%+Sand 50%

Quartz SiO2

Calcite CaCO3


Clorite A5-6T40Z8-10 A:Al, Fe2+,Fe3+, Mn, Mg, Li, or Ni.T:Al, Fe3+, Si or theircombinationZ: O or OH.

PC 60%+FA 40%+ZER 50%+Sand 50%

Quartz SiO2

Calcite CaCO3


Clorite A5-6T40Z8–10A:Al, Fe2+, Fe3+,Mn, Mg, Li, or Ni.T:Al, Fe3+, Si or theircombinationZ: O or OH.

L 10%+ZER 90% Calcite CaCO3

Gypsum CaSO4.2H2OQuartz SiO2


Anglesite PbSO4


Susannite Pb4SO4(CO3)2(OH)L 20%+ZER 80% Calcite CaCO3



Anglesite PbSO4


Susannite Pb4SO4(CO3)2(OH)

272 M. Erdem, A. Özverdi / Hydrometallurgy 105 (2011) 270–276

Table 2 (continued)


L 30%+ZER 70% Calsite CaCO3



Anglesite PbSO4



Gypsum CaSO4.2H2OPortlandite Ca(OH)2Cerrusite PbCO3

Quartz SiO2

Maghemite Fe2O3

Anglesite PbSO4


Gypsum CaSO4.2H2OPortlandite Ca(OH)2Cerrusite PbCO3

Quartz SiO2

Maghemite Fe2O3

Anglesite PbSO4

Susannite Pb4SO4(CO3)2(OH)PC 90%+L 10%+ZER 50%+Sand 50%

Calcite CaCO3

Quartz SiO2

Portlandite Ca(OH)2Cerrusite PbCO3

Maghemite Fe2O3

Anglesite PbSO4

Susannite (minor) Pb4SO4(CO3)2(OH)Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2O

PC 80%+L 20%+ZER 50%+Sand 50%

Calcite CaCO3

Gypsum (minor) CaSO4.2H2OPortlandite Ca(OH)2Cerrusite PbCO3

Quartz SiO2

Maghemite Fe2O3

Anglesite PbSO4

Susannite Pb4SO4(CO3)2(OH)Ettringite (minor) Ca6Al2(SO4)3(OH)12.26H2O

PC 70%+L 30%+ZER 50%+Sand 50%

Calcite CaCO3

Gypsum CaSO4.2H2OPortlandite Ca(OH)2Cerrusite (minor) PbCO3

Quartz SiO2

Maghemite Fe2O3

Anglesite PbSO4


PC 60%+L 40%+ZER 50%+Sand 50%

Calcite CaCO3

Gypsum CaSO4.2H2OPortlandite Ca(OH)2Cerrusite (minor) PbCO3

Quartz SiO2

Maghemite Fe2O3

Anglesite PbSO4


Table 3Compressive strengths of the some samples solidified/stabilized by PC, PC+FA, PC+Lafter 28 days of curing.

S/S product Strength (MPa)

PC 10%+ZER 90% 0.14PC 20%+ZER 80% 0.19PC 30%+ZER 70% 0.31PC 40%+ZER 60% 0.47PC 50%+ZER 50% 0.49PC 90%+FA 10%+ZER 50%+Sand 50% 3.31PC 80%+FA 20%+ZER 50%+Sand 50% 2.26PC 70%+FA 30%+ZER 50%+Sand 50% 1.88PC 60%+FA 40%+ZER 50%+Sand 50% 1.62PC 90%+L 10%+ZER 50%+Sand 50% 1.79PC 80%+L 20%+ZER 50%+Sand 50% 1.64PC 70%+L 30%+ZER 50%+Sand 50% 1.31PC 60%+L 40%+ZER 50%+Sand 50% 0.88


3.2. Compressive strength

PC, FA, L and theirmixtureswere used for S/S of the ZER. The cracksand disintegrations were observed in the specimens prepared withonly FA and L during the curing period. In order to obtain a monolithicsolid of high structural integrity, PC was the best binding materialamong these materials. Therefore, compressive strength of the S/Ssamples prepared with PC and PC-based mixtures were measured.The results are shown in Table 3.

0.34 MPa or 50 psi is recommended compressive strength valuefor the S/S products for the disposal in secured landfill (Malviya andChaudhary, 2006). As seen from Table 3, the samples containing lowerthan PC 40% did not attain the strength criteria for S/S of the ZER due

to their lower compressive strength. Similar results have been foundby Zain et al. They have been reported that the lower strengths of theZER containing mortars can be attributed to the set-inhibitingproperties of the heavy metals (Zain et al., 2004). For the desiredproperties, it can be stated that theminimum PC amount is 40 percentof the mixture.

3.3. Batch leaching tests

In order to clarify dissolution properties of the solidified/stabilizedsamples in the solutions having different compositions, batch leachingtests were carried out in the solutions having pHs of which are in therange of 3–12. The results obtained are shown in Tables 4 and 5.

Release of Pb and Zn showed different properties greatlydepending on the S/S reagent used. The PC-based samples are morestable under the investigated conditions. The results of the testsapplied demonstrate that relatively small additions of PC and FA orcombination of them drastically reduce the heavy metal release.While dissolved Pb concentrations of all the samples are below thedetection limits, Zn released lower than 0.48 mg/l in the solutionshaving pH of 3 and 4. For the samples solidified/stabilized by usingonly FA, Zn dissolution was not determined, however, at pH 3, 4 and12, Pb released up to 7.21 mg/l. The high concentrations of Pb and Znwere determined in the all leachates of the samples solidified/stabilized by using only lime. This situation can be attributed to thehigh alkaline properties of the lime. In order to prove this idea, finalpHs of the solutions were measured and compared (Fig. 1). pH of theall solutions (except for L 10%) was about 12.5. The higherconcentrations of Pb and Zn determined in the all high pHs can beassociated with the amphoteric behavior of these elements. Similarresults have been found by Geysen et al. (2004a,b) who haveinvestigated comparison of immobilization of air pollution controlresidues with cement and silica. For the S/S reagents investigated, itcan be concluded that the lime is not proper S/S reagent and the S/Sefficiencies decreases in the sequence PCNFANNL. But, PC or FA mustbe optimized depending on their costs before prefer of them.

3.4. Toxicity characteristic leaching procedure (TCLP)

In our previous study, it has been determined that the TCLP Pb andCd concentrations for untreated ZER were 65.11 and 2.88 mg/l,respectively, which were higher than the regulatory limits of 5 mg/lfor Pb and 1 mg/l for Cd. Table 6 shows the TCLP test results of thesolidified/stabilized products of thiswaste. The PC and PC-based and theminimum 30% FA treatments reduced the TCLP concentration to lessthan4.27 mg/l. In contrast to, thehighTCLP leachabilitieswereobservedfor the S/S samples containingonly lime and lower than 30%flayash dueto amphoteric behavior of these elements. These values are alsoconsistent with that of the batch leaching test.

Table 4The variations of Pb concentrations released from the solidified/stabilized samples depending on pH by batch leaching tests (liquid/solid: 20; contact time: 18±2 h; temperature:25 °C).

S/S Product Pb concentrations, mg/L

pH

3 4 5 6 7 8 9 10 11 12

PC 10%+ZER 90% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC 20%+ZER 80% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC 30%+ZER 70% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC 40%+ZER 60% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC 50%+ZER 50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLFA 10%+ZER 90% 7.21 5.06 UDL UDL UDL UDL UDL UDL UDL 1.08FA 20%+ZER 80% 4.93 2.94 UDL UDL UDL UDL UDL UDL UDL 0.96FA 30%+ZER 70% 3.58 1.16 UDL UDL UDL UDL UDL UDL UDL 1.01FA 40%+ZER 60% 3.22 0.90 UDL UDL UDL UDL UDL UDL UDL UDLFA 50%+ZER 50% 3.19 0.42 UDL UDL UDL UDL UDL UDL UDL UDLPC90%+FA10%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL 0.67PC80%+FA20%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC70%+FA30%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC60%+FA40%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLL 10%+ZER 90% 4.32 3.73 3.89 4.47 4.40 4.29 4.75 4.84 4.62 4.77L 20%+ZER 80% 5.87 5.52 5.52 5.46 5.16 5.36 5.38 5.21 5.17 5.21L 30%+ZER 70% 6.49 6.32 5.96 5.90 5.50 5.12 5.24 5.54 5.34 5.77L 40%+ZER 60% 6.97 6.63 6.37 5.91 5.50 5.48 5.63 5.48 5.28 5.46L 50%+ZER 50% 8.69 8.02 6.67 6.52 6.24 6.35 6.77 6.75 7.55 7.93PC90%+L10%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC80%+L20%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC70%+L30%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDLPC60%+L40%+ZER50%+Sand50% UDL UDL UDL UDL UDL UDL UDL UDL UDL UDL

UDL: under the detection limits.


It has been determined that the Pb in the form of anglesite[Pb4SO4] which is main contaminant in the ZER was transformed intosusannite [Pb4SO4(CO3)2(OH)2] and cerrusite [PbCO3] minerals by S/Streatments (Table 2). The solubility products of anglesite, susanniteand cerrusite are 2.53×10−8, 7.40×10−14 and 1.08×10−5, respec-tively. Cerrusite is very poorly soluble indicated by the low solubilityproduct, unlike susannite more soluble due to its relatively highersolubility product. Susannite is one of themainminerals formed in thelime-based treatments. Therefore, dissolution of the susannite fromthese S/S samples could be responsible for lead.

Table 5The variations of Zn concentrations released from the solidified/stabilized samples dependin25 °C).

S/S product Zn concentrations, mg/L

pH

3 4 5 6

PC 10%+ZER 90% 0.28 0.22 UDL UPC 20%+ZER 80% 0.20 UDL UDL UPC 30%+ZER 70% UDL UDL UDL UPC 40%+ZER 60% UDL UDL UDL UPC 50%+ZER 50% UDL UDL UDL UFA 10%+ZER 90% UDL UDL UDL UFA 20%+ZER 80% UDL UDL UDL UFA 30%+ZER 70% UDL UDL UDL UFA 40%+ZER 60% UDL UDL UDL UFA 50%+ZER 50% UDL UDL UDL UPC90%+FA10%+ZER50%+Sand50% UDL UDL UDL UPC80%+FA20%+ZER50%+Sand50% UDL UDL UDL UPC70%+FA30%+ZER50%+Sand50% UDL UDL UDL UPC60%+FA40%+ZER 50%+Sand 50% 0.48 UDL UDL UL 10%+ZER 90% 0.41 0.47 0.42 0L 20%+ZER 80% 1.24 1.76 0.33 2L 30%+ZER 70% 1.74 1.90 1.94 1L 40%+ZER 60% 4.64 2.10 1.88 1L 50%+ZER 50% 3.18 1.86 1.61 1PC90%+L10%+ZER50%+Sand50% UDL UDL UDL UPC80%+L20%+ZER50%+Sand50% UDL UDL UDL UPC70%+L30%+ZER50%+Sand50% UDL UDL UDL UPC60%+L40%+ZER50%+Sand50% UDL UDL UDL U


According to results obtained, it can be stated that the all S/Smethods applied except for only lime and lower than 30% flay ashtreatments are proper for S/S of the ZER.

3.5. Synthetic precipitation leaching procedure (SPLP)

SPLP is frequently used to assess the risk to groundwater posed bycontaminated soils (USEPA, 1994) and in the risk assessment processfor determining beneficial use of solid wastes (DEP, 1998, 2001). SPLPleachate concentrations are compared to the groundwater quality

g on pH by batch leaching tests (liquid/solid: 20; contact time: 18±2 h; temperature:

7 8 9 10 11 12

DL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL 0.22.42 0.34 0.41 0.40 0.36 0.38 0.43.12 1.40 1.50 1.82 1.06 1.62 2.14.86 2.18 2.14 2.01 2.09 0.54 2.15.85 1.85 1.85 1.86 1.82 1.82 1.75.25 1.17 0.68 1.98 1.98 1.95 1.61DL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDLDL UDL UDL UDL UDL UDL UDL

Table 6TCLP test results of solidified/stabilized samples.

S/S product Released metal concentration, mg/L

Pb Zn Cd Mn Cu

PC 10%+ZER 90% 0.90 UDL UDL UDL UDLPC 20%+ZER 80% 0.63 UDL UDL UDL UDLPC 30%+ZER 70% 0.40 UDL UDL UDL UDLPC 40%+ZER 60% 0.18 UDL UDL UDL UDLPC 50%+ZER 50% UDL UDL UDL UDL UDLFA 10%+ZER 90% 8.04 46.33 0.84 UDL UDLFA 20%+ZER 80% 5.28 40.72 0.26 UDL UDLFA 30%+ZER 70% 3.12 31.50 UDL UDL UDLFA 40%+ZER 60% 3.06 29.82 UDL UDL UDLFA 50%+ZER 50% 3.24 26.18 UDL UDL UDLL 10%+ZER 90% 62.50 182 1.08 0.42 0.61L 20%+ZER 80% 69.80 147 UDL UDL UDLL 30%+ZER 70% 76.41 113 UDL UDL UDLL 40%+ZER 60% 80.36 94 UDL UDL UDLL 50%+ZER 50% 79.50 86 UDL UDL UDLPC90%+FA10%+ZER50%+Sand50% UDL UDL UDL UDL UDLPC80%+FA20%+ZER50%+Sand50% UDL UDL UDL UDL UDLPC70%+FA30%+ZER50%+Sand50% UDL UDL UDL UDL UDLPC60%+FA40%+ZER50%+Sand50% 1.60 0.25 UDL UDL UDLPC90%+L10%+ZER50%+Sand50% UDL 2.54 UDL UDL UDLPC80%+L20%+ZER50%+Sand50% 0.96 2.93 UDL UDL UDLPC70%+L30%+ZER50%+Sand50% 3.08 5.22 UDL UDL UDLPC60%+L40%+ZER50%+Sand50% 4.27 9.14 UDL UDL UDL


Table 7SPLP test results of ZER and solidified/stabilized samples.

S/S product Leached metal concentration, mg/L

Pb Zn Cd Mn Cu

ZER 7.02 61.20 1.77 0.93 UDLPC 10%+ZER 90% 3.51 0.11 0.2 UDL UDLPC 20%+ZER 80% 2.81 0.11 UDL UDL UDLPC 30%+ZER 70% 2.25 0.09 UDL UDL UDLPC 40%+ZER 60% 2.45 0.19 UDL UDL UDLPC 50%+ZER 50% 1.09 0.20 UDL UDL UDLFA 10%+ZER 90% 5.33 22 UDL UDL UDLFA 20%+ZER 80% 3.12 7.0 UDL UDL UDLFA 30%+ZER 70% 2.91 1.13 UDL UDL UDLFA 40%+ZER 60% 2.90 0.94 UDL UDL UDLFA 50%+ZER 50% 1.40 1.06 UDL UDL UDLL 10%+ZER 90% 12.54 6.24 UDL UDL UDLL 20%+ZER 80% 9.81 8.21 UDL UDL UDLL 30%+ZER 70% 8.68 8.96 UDL UDL UDLL 40%+ZER 60% 9.11 11.52 UDL UDL UDLL 50%+ZER 50% 13.84 18.44 UDL UDL UDLPC 90%+FA 10%+ZER 50%+Sand 50% UDL UDL UDL UDL UDLPC 80%+FA 20%+ZER 50%+Sand 50% 0.40 UDL UDL UDL UDLPC 70%+FA 30%+ZER 50%+Sand 50% 0.92 UDL UDL UDL UDLPC 60%+FA 40%+ZER 50%+Sand 50% 1.03 UDL UDL UDL UDLPC 90%+L 10%+ZER 50%+Sand 50% UDL 2.94 UDL UDL UDLPC 80%+L 20%+ZER 50%+Sand 50% 2.29 5.31 UDL UDL UDLPC 70%+L 30%+ZER 50%+Sand 50% 3.80 6.45 UDL UDL UDLPC 60%+L 40%+ZER 50%+Sand 50% 4.04 6.73 UDL UDL UDL



standards. The SPLP results exceeded the drinking water standards,most notably for Pb (Table 7). Therefore, the samples solidified andstabilized should not be disposed in unlined landfills.

4. Conclusions

Following conclusions can be drawn from the results of the presentstudy dealing with the solidification and stabilization of the zincextraction residue;

(1) In order to obtain a monolithic solid of high structural integrity,PC was found as the best binding material among the materialstried and the minimum amount of PC was 40% of the mixture.

(2) Release of Pb and Zn showed different properties greatlydepending on the S/S reagent used. The ZER can be safelysolidified/stabilized in the cement and cement-based S/Ssystem. It has been determined that the lime was not properas an S/S reagent and the S/S efficiencies decreased in thesequence PCNFANNL.

10,0

10,5

11,0

11,5

12,0

12,5

13,0

2 3 4 5 6 7 8 9 10 11 12 13

L 10% + ZER 90% L 20% + ZER 80%

L 30% + ZER 70% L 40% + ZER 60%

L 50% + ZER 50%

pHinitial

pHfi

nal

Fig. 1. pH variations in the batch leaching solutions obtained from the experimentscarried out with lime-based S/S samples.

(3) When the PC and PC- based combinations and the minimum30% FAwere used as a S/S reagent, the extractable heavymetalscould be successfully immobilized. Their concentrations de-creased to less than TCLP limits.

(4) Pb in the form of anglesite which is main contaminant in theZER was transformed into susannite [Pb4SO4(CO3)2(OH)2] andcerrusite [PbCO3] minerals by S/S treatments.

Acknowledgements

This study was financed by the Scientific and TechnologicalResearch Council of Turkiye (TUBITAK) under the project number of107Y139.

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