Treatment of copper industry waste and production of sintered glass ...

Copyright © ISWA 2006

Waste Manage Res 2006: 24: 234–241 Printed in UK – all right reserved

Waste Management & Research

ISSN 0734–242X

Treatment of copper industry waste and production of sintered glass–ceramic Copper waste is iron-rich hazardous waste containing heavy metals such as Cu, Zn, Co, Pb. The results of leaching tests show that the concentration of these elements exceeds the Turkish and EPA regulatory limits. Consequently, this waste cannot be disposed of in its present form and therefore requires treatment to stabilize it or make it inert prior to disposal. Vitrification was selected as the technology for the treatment of the toxic waste under investigation. During the vitrification process significant amounts of the toxic organic and inorganic chemical compounds could be destroyed, and at the same time, the metal species are immobilized as they become an integral part of the glass matrix. The copper flotation waste samples used in this research were obtained from the Black Sea Copper Works of Samsun, Turkey. The samples were vitrified after being mixed with other inorganic waste and materials. The copper flotation waste and their glass–ceramic products were characterized by X-ray analysis (XRD), scanning electron microscopy and by the toxicity characteristic leaching procedure test. The products showed very good chemical durability. The glass–ceramics fabricated at 850°C/2 h have a large application potential especially as construction and building materials.

Semra Çoruh Osman Nuri Ergun Department of Environmental Engineering, Ondokuz Mayis University, Samsun, Turkey

Ta-Wui Cheng Department of Materials & Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwan

Keywords: Copper flotation waste, vitrification, glass–ceramic, heavy metals, wmr 857–5

Corresponding author: Semra Çoruh, Department of Environmental Engineering, Ondokuz Mayis University, 55139 Samsun, Turkey. Tel: +90 362 457 60 20 ext1328; fax: +90 362 457 60 35; e-mail: [email protected] DOI: 10.1177/0734242X06062600 Received 6 April 2005; accepted in revised form 28 November 2005

Introduction Copper occasionally occurs pure and is found in many minerals such as cuprite, malachite, bornite, chalcopyrite, covellite and azurite. The most important types of copper ores are the sulphides, oxides and carbonates. From these, copper is obtained by smelting, leaching and by electrolysis. Copper flotation waste which is the product of pyrometallurgical production of copper from copper ores contain materials such as iron, alumina, calcium oxide, silica, etc. According to Gorai et al. (2003), about 2.2 tonnes of copper flotation waste is generated for each ton of metal production. Consequently, approximately 24.6 million tonnes of copper flotation waste is generated each year, based on the world copper

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production. Copper slag and the flotation waste are generally disposed of without any prior solid waste treatment in areas around the industrial facility at which they are generated. Dumping of such large amounts of copper slag causes economic, environmental and space problems and therefore, governments have implemented policies that give mining and metallurgical companies the responsibility for reducing the volume of solid waste deposition by promoting the material recycling and re-utilization. Due to these strict environmental regulations and the reduction or eventual elimination of the cost of copper slag deposition, copper smelters are looking for technological innovation, which involves utilization

Treatment of copper industry waste and production of sintered glass–ceramic

of the copper slag (Kersch et al. 2004, Gonzales et al. 2005). In particular, the development of new ceramic, glass and glass– ceramic materials, made by recycling waste, is of specific importance (Scarinci et al. 2000). Vitrification is one of the best technical processes for the immobilization and destruction of environmentally dangerous components in waste materials. Furthermore, the vitrification process usually results in a large reduction in the volume of the waste, with evident benefits in terms of long-term storage or dumping. Toxic organic and inorganic chemical compounds are destroyed and hazardous metal components in the waste are converted into non-hazardous oxides by the vitrification process at temperatures above 1300°C. The metal species present in the waste are immobilized as they become an integral part of the glass matrix (Karamanov et al. 1999, Rincon et al. 1999). It is necessary to know the chemical composition of the waste in order to design the mixture to be vitrified and consequently for the characteristics of the glass or glass–ceramic products resulting from the vitrification. In this perspective, it is important that waste materials of different origin and composition are simultaneously vitrified, so that each of them may contribute the appropriate quantities of vitrifying (SiO2, Al2O3, …), melting (Na2O, K2O, …) and stabilizing (CaO, MgO, ZnO, PbO, …) agents in the final glass in order that suitable physical–chemical properties are obtained (Barbieri et al. 2000). The Black Sea Copper Works, which is situated in the metropolitan city centre of Samsun, was established in 1973 and has an annual capacity of 37 800 tonnes of blister copper, which is obtained by treating 170 000 tonnes of lump sulphide ores with 22% Cu grade. The obtained slag is treated by a milling–flotation process, which each year generates increasing amounts of copper flotation waste and has reached about 150 000 tonnes year–1 for the last 10 years. As a result of this activity, about 1.5–2 million tonnes of slag and copper flotation waste have been disposed of on the flood plain of the Yesilirmak River Delta, currently without any environmental pollution control. Hence, as a result of leaching, metals such as Cu, Zn, Co, Fe and Pb are present in the waste pollute surface and groundwater resources (Pelino et al. 2004). In a recently conducted study, the characterization of the microstructure of the vitrified copper flotation waste product and the chemical composition of a glass and glass–ceramic material obtained from copper flotation waste was investigated. The microstructure materials were characterized by the toxicity characteristic leaching procedure (TCLP). The TCLP was selected as the batch leaching test, because it simulates conditions similar to those prevailing at landfills that have acidic drainage (US EPA 1989). X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were used to characterize the micro-

structure and chemical composition of heat-treated copper flotation waste.

Experimental procedure The samples of copper flotation waste were obtained from The Black Sea Copper Works in Samsun, Turkey. The other waste and the raw material used in this study were fly ash and perlite. The fly ash was obtained from Kütahya Seyitömer thermal plant and the perlite was obtained from Etibank Izmir Comaovasi Perlit Factory, both in Turkey. Table 1 illustrates the chemical composition of the investigated perlite as raw material and the copper and fly ash waste. The chemical compositions of the waste materials were evaluated by using X-ray fluorescence techniques (Spectro-Xepos). Copper flotation waste has a black colour and glassy appearance and its specific gravity was 3100 kg m–3. The absorption capacity of the waste material was typically very low (0.13%). As can be seen in Table 1, the copper flotation waste contained significant levels of Fe2O3 (67.68%) and SiO2 (24.87%), whereas the contents of other metal oxides were much less than 10%. The hazardous oxides in the copper flotation waste included ZnO, CuO, PbO and CoO. The crystalline phase composition of the material was investigated using X-ray diffractometry (RIGAKU, D/Max-IIIC) with CuKα radiation. The X-ray diffraction pattern shown in Table 1: Chemical composition (wt. %) of the copper flotation waste and other materials. Copper flotation waste

Perlite

SiO2

24.87

72.90

59.09

Fe2O3a

67.68

0.53

12.06

Al2O3

0.92

11.90

17.05

TiO2

0.08

–

–

CaO

0.69

0.79

9.44

CuO

0.98

–

–

ZnO

2.78

–

–

PbO

0.21

–

–

Cr2O3

0.12

–

–

SO3

2.18

–

0.98

K2O

0.48

4.47

0.59

MgO

0.36

0.18

1.33

BaO

0.10

–

–

CoO

0.21

–

–

Na2O

–

3.29

–

P 2O 5

–

0.02

–

MnO

0.12

0.05

–

LOIb

–

5.87

a b

Fly ash

Iron oxides are present as Fe2O3. Loss on ignition.


235

S. Çoruh, O.N. Ergun, T.-W. Cheng

Fig. 1: XRD patterns of the copper flotation waste.

Table 2: Weight % component ratios in the studied glass compositions. Copper flotation waste

Perlite

Fly ash

Na2CO3

SiO2

CaCO3

MgO

100

–

–

–

–

–

–

F60

60

30

–

10

–

–

–

F160

60

–

30

10

–

–

–

F260

60

–

20

5

5

8

2

F

Figure 1 revealed fayalite (Fe2SO4), magnetite (Fe3O4), copper sulphide ((Fe, Cu) S2) and cuprospinel (Cu Fe2O4) and SiO2 to be the main phases present in the slag. As the metals are most stable in oxide and silicate forms, construction material produced from copper slag is very resistant against corroding. Knowledge of the chemical composition of the waste is necessary in order to design the input mixture for vitrification and consequently the characteristics of the glass and glass– ceramic products produced. As the copper flotation waste does not contain enough glass–network-forming agents, it was mixed with raw materials and other residues in order to obtain a glass with suitable properties. The similarity of perlite to sodium feldspar means that it is also a suitable material for the glass and ceramic industry. This study therefore dealt mainly with the four most representative investigated glass compositions, namely F, F60, F160 and F260. The mixtures for vitrification were mixed together in the ratios reported in Table 2. The chemical composition of the four glass mixtures obtained is shown in Table 3.

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Table 3: Chemical composition (wt. %) of the investigated glasses F60

F160

F260

SiO2

47.10

43.30

44.30

Fe2O3

28.72

31.82

29.29

Al2O3

6.20

7.10

5.30

CaO

0.62

3.84

9.78

Na2O

10.34

9.02

4.32

CuO

1.61

0.63

0.59

ZnO

0.70

0.72

0.71

MgO

0.57

1.02

2.88

P 2O 5

0.01

0.01

0.02

K2O

2.40

1.46

1.14

The glasses are non-crystalline substances formed from a melt by cooling. They can be regarded as supercooled liquids and their crystallization can be achieved by controlling the nucleation and crystal growth rates. The materials investigated were placed in a graphite crucible and induction-heated on


air. The molten samples were kept at 1550°C for 30 min to ensure complete melting. They were subsequently quenched in water to obtain glass frit. The frits were dried and ground to grain sizes below 400 mesh. The frits were dried in an oven at 150°C for 3 h to eliminate the moisture. The ground samples were pressed into 1 cm × 1 cm × 0.2 cm stainless steel moulds without using any binder and applying a pressure of 250 kg cm–2. The pressed samples were sintered for 2 h at different temperatures such as 650, 750, 850, 950, and 1050°C and then cooled down to room temperature. The obtained glass–ceramics were subjected to various analytical procedures: the chemical analysis was performed by using X-ray fluorescence (XRF) spectroscopy; the crystalline phase of the material was investigated using X-ray diffractometry (XRD); the chemical durability was assessed by TCLP leaching tests; microstructure/morphology observation was performed by using a scanning electron microscopy (SEM).

Result and discussion TCLP test on copper flotation waste and vitrified waste The metal ions selected for the study were Cu, Zn, Pb, Co and Cr. They were selected because of their presence in the copper flotation waste and also their toxic nature, which requires proper handling under the Turkish Environmental Quality Regulations. The TCLP is used by the EPA as the basis for the promulgation of best demonstrated available technologies (BDAT) treatment standards included in the land disposal restrictions programme. The copper flotation waste samples were subjected to US EPA TCLP tests to determine the leachability characteristics for heavy metals in the raw waste and in waste which has been treated thermally at several temperatures such as 200, 400, 600, 800, 1000 and 1200°C. This procedure allows the chemical resistance of the waste and glass–ceramic materials to be assessed. The raw waste and waste treated thermally at different temperatures were exposed to the TCLP test. To obtain TCLP extracts, 5 g copper flotation waste was agitated in glass jars

Table 4: Changes in Cu, Zn, Pb, Co and Cr concentrations (mg L–1) in the TCLP leaching test solutions from raw copper flotation waste as a function of treatment temperature. Thermal treatment temperature (°C)

Cu

Zn

Pb

Co

Cr

Room temperature

138

17

1.5

0.8

0.2

200

152

18.5

1.8

1.3

0.4

400

285

28

2.1

1.8

0.9

600

345

54

23

3.5

1.2

800

18

11

21

3.9

0.9

1000

5.2

4

3.2

0.5

0.1

1200

2.5

2

2.8

0.3

0.07

containing 100 mL of extracting medium for the specified time period of 18 h. The pH adjustment was made with 0.1 N acetate buffer containing 64.3 mL of 1.0 N sodium hydroxide (NaOH) and 5.7 ml glacial acetic acid in 1 L water. Under this condition, the final pH of the solution was buffered at 4.93 ± 0.02. The copper flotation waste was heated for 3 h at different temperatures to determine the amount of metal released as a function of rising temperature. According to literature the metal solubility in copper flotation waste containing both oxide and sulphide of Cu decreases with increasing treatment temperature (Spira 1969). The Cu, Zn, Pb, Co and Cr leachate concentrations for the raw waste and the waste treated at 200, 400, 600, 800, 1000 and 1200°C are summarized in Table 4. The results indicated leachate concentrations of 138 mg L–1 for Cu, 17 mg L–1 for Zn, 1.5 mg L–1 for Pb, 0.8 mg L–1 for Co, and 0.2 mg L–1 for Cr, respectively. The values for Cu, Zn and Pb exceed the limits of Turkish standards and EPA standards (see Table 5). As expected, the release of Cu in raw copper flotation waste was considerably higher than the releases of Zn, Co and Cr. In this study, metals released from the copper flotation waste increased with increasing temperature of treatment up to 600°C. At this temperature, Cu, Zn, Pb, Co and Cr releases were found to be 345, 54, 23, 3.5 and 1.2 mg L–1, respectively. Metal releases decreased for samples treated at temperatures of 800°C or higher due to the glassy matrix obtained, and were lowest at a

Table 5: TCLP leaching test results for the waste glasses vitrified at 1550°C. Elements Cu

F (mg L–1)

F60 (mg L–1)

F160 (mg L–1)

F260 (mg L–1)

Turkish limits (mg L–1)

EPA limitsa (mg L–1)

0.13

≤ 0.007

0.011

0.024

3

nr

Zn

0.28

0.59

0.067

0.34

2

4.30

Pb

≤ 0.005

≤ 0.003

≤ 0.004

≤ 0.002

0.4

0.75

Co

0.35

0.38

0.44

0.04

nr

nr

Cr (VI)

0.13

0.15

0.14

0.13

5

0.60

a Federal Register V63 ≠ 100, 28 May 1998. nr, not regulated.


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Fig. 2: XRD patterns of copper flotation waste (650; 750; 850 and 950°C). H, haematite; M, maghamite; P, pyroxene; F, fayalite.

treatment temperature of 1200°C. The levels of Cu, Zn, Pb, Co and Cr released from samples treated at 1200°C were 2.5, 2, 2.8, 0.3 and 0.07 mg L–1, respectively. The results of leaching analysis of vitrified materials (waste glasses) at 1550°C are summarized in Table 5 and show that Cu, Zn, Pb, Co and Cr releases from F and F60 samples were found to be 0.13, 0.28, ≤ 0.005, 0.35 and 0.13; and ≤ 0.007, 0.59, ≤ 0.003, 0.38 and 0.15, respectively. Similar results were also obtained for the F160 and F260 samples. The levels of the analysed elements were within the US EPA and Turkish regulatory limits. Only small amounts of Cu released from the vitrified mixed copper flotation waste were assessed. This behaviour can be explained due to the formation of stable crystal phases with an increasing content of SiO2 in the residual glass. Similar results have also been reported for a zinc– hydrometallurgy waste in Italy (Pisciella et al. 2001; Pelino et al. 2002; Park & Heo 2002). Characterization of crystalline phases in the glass–ceramic By thermal treatment of the glasses, nucleation and crystallization took place in a controlled manner, leading to the for-

238


mation of crystalline phases throughout the bulk of the sample. In the kinetics of glass crystallization, the nucleation process requires particular attention since an efficient rate of nucleation greatly affects the final properties of the glass– ceramic. After the re-crystallization experiments, the samples were investigated by using XRD and SEM. Macroscopically, the samples identified as F, F60, F160 and F260 showed a tendency from reddish brown to chocolate brown and darker with increasing temperatures and annealing times. The crystallization of a super-cooled liquid is controlled by the rate of nucleation and crystal growth. XRD analysis of the bulktreated glass–ceramic samples showed different tendencies towards crystallization as a function of thermal treatment temperatures. The XRD results for flotation waste are shown in Figure 2. The XRD spectrum of the glass–ceramic samples shows the formation of magnetite spinel and pyroxene solid solution (FeO.SiO2, Fe3O4 and Ca (Fe, Mg) (SiO3)2). Figure 3 shows that different crystalline phases are present depending on the glass–ceramic composition and thermal treatment performed, but the pyroxene (FeOx.MgO1–x.CaO.2SiO2), diopside (Ca(Mg, Al) (Si, Al)2O6) and wollastonite (W)


Fig. 3: XRD patterns recorded on F, F60, F260 glass-ceramics treated at 850°C for 2 h. H, hematite; M, maghamite; P, pyroxene; W, wollastonite.

(CaSiO3) are the main phases present in the glass–ceramic samples. SEM observations of microstructure materials after heat treatment at several temperatures were performed. SEM results

of F260 samples treated at various temperatures (650, 750, 850, 950 and 1050°C) and F, F60, F260 samples treated at 850°C are shown in Figures 4 and 5, respectively. The influence of the sintering temperature on the evolution of the

Fig. 4: Scanning electron microscopic (SEM) micrograph of microstructure material sample F260 heat treated for 2 h at (a) 650°C; (b) 750°C; (c) 850°C; (d) 950°C; (e) 1050°C.


239


Fig. 5: Scanning electron microscopic (SEM) micrograph of F, F60, F260 microstructure material sample heat treated for 2 h at 850°C.

porous structure can obviously be assumed. This microstructure seems to indicate that the crystal size increased with increasing heat-treatment temperature. When the microstructure materials were heat treated at 1050°C, both the crystal growth rate and crystal size improved. As one possibility, rapid heating provides better sintering. Another possibility for controlling the relative rates of sintering and crystallization of the glass powders is to chemically treat the glass particle surfaces (Boccaccini 2000).

Conclusions Treatment and characterizations of the copper flotation waste by using vitrification technology have been carried out. Vitrification is one of the most promising technological options and recognized as an environmentally acceptable solution for the treatment of industrial waste since it improves the potential chemical resistance of the product and also reduces the volume of the waste for disposal. An accurate selection and adequate ratios of the waste materials used allows the properties of the vitrification product to be varied. In this study, the copper flotation waste obtained from The Black Sea Copper Works of Samsun, Turkey was thermally treated and vitrified by itself and with the addition of other waste materials and reagents. Copper flotation waste was heat-treated at different temperatures and it was found that metal releases decreased for samples treated at temperatures higher than 800°C because of the formation of a glassy

240


matrix, and that releases were minimal at a treatment temperature of 1200°C. Using TCLP procedures the releases of Cu, Zn, Pb, Co and Cr for samples treated at 1200°C were 2.5, 2, 2.8, 0.3 and 0.07 mg L–1, respectively. The amounts of Cu, Zn and Cr released for samples treated at this temperature did not exceed the limits of Turkish and EPA standards. In this regard, heat-treated copper flotation waste cannot be classified as a hazardous waste under the principles of Resource Conservation and Recovery Act (RCRA). Cu, Zn, Pb, Co and Cr releases from F, F60, F160 and F260 samples were found to be 0.13, 0.28, ≤ 0.005, 0.35 and 0.13 mg L–1; ≤ 0.007, 0.59, ≤ 0.003, 0.38 and 0.15 mg L–1; 0.011, 0.067, ≤ 0.004, 0.44 and 0.14 mg L–1; and 0.024, 0.34, ≤ 0.002, 0.04 and 0.13 mg L–1, respectively. The glasses obtained, particularly with fly ash perlite and additives SiO2, CaCO3 and MgO were effective in confining heavy metal ions from the leaching. These glasses showed good chemical resistance and passed the US EPA and Turkish regulatory limits for TCLP tests. According to Scarinci et al. (2000), a similar result was also reported for production of glass fibres using industrial and natural waste materials. The results clearly show that glass and glass–ceramic products of acceptable quality can be produced by vitrification of the copper flotation waste. Microstructure materials with improved physical and mechanical properties were obtained after heat treatment at low temperatures such as 650 and 750°C. Microstructure materials have a wide range of potential applications especially for construction and building materials.


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