Immobilization of heavy metals in electroplating sludge by biochar and

Environ Sci Pollut Res DOI 10.1007/s11356-016-6621-5

RESEARCH ARTICLE

Immobilization of heavy metals in electroplating sludge by biochar and iron sulfide Honghong Lyu 1 & Yanyan Gong 1,2,3 & Jingcshun Tang 1,2,3 & Yao Huang 1 & Qilin Wang 4

Received: 20 January 2016 / Accepted: 3 April 2016 # Springer-Verlag Berlin Heidelberg 2016

Abstract Electroplating sludge (ES) containing large quantities of heavy metals is regarded as a hazardous waste in China. This paper introduced a simple method of treating ES using environmentally friendly fixatives biochar (BC) and iron sulfide (FeS), respectively. After 3 days of treatment with FeS at a FeS-to-ES mass ratio of 1:5, the toxicity characteristic leaching procedure (TCLP)-based leachability of total Cr (TCr), Cu(II), Ni(II), Pb(II), and Zn(II) was decreased by 59.6, 100, 63.8, 73.5, and 90.5 %, respectively. After 5 days of treatment with BC at a BC-to-ES mass ratio of 1:2, the TCLP-based leachability was declined by 35.1, 30.6, 22.3, 23.1, and 22.4 %, respectively. Pseudo first-order kinetic model adequately simulated the sorption kinetic data. Structure and morphology analysis showed that adsorption, electrostatic attraction, surface complexation, and chemical precipitation were dominant mechanisms for heavy metals immobilization by BC, and that chemical precipitation (formation of metal sulfide and hydroxide precipitates), iron exchange (formation of CuFeS 2 ), and surface complexation were mainly Responsible editor: Angeles Blanco * Yanyan Gong [email protected] * Jingcshun Tang [email protected]

1

College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China

2

Key Laboratory of Pollution Processes and Environmental Criteria (Ministry of Education), Tianjin 300071, China

3

Tianjin Engineering Center of Environmental Diagnosis and Contamination Remediation, Tianjin 300071, China

4

Advanced Water Management Centre, The University of Queensland, St Lucia, Queensland 4072, Australia

responsible for heavy metals removal by FeS. Economic costs of BC and FeS were 500 and 768 CNY/t, lower than that of Na2S (940 CNY/t). The results suggest that BC and FeS are effective, economic, and environmentally friendly fixatives for immobilization of heavy metals in ES before landfill disposal. Keywords Heavy meals . Immobilization . Electroplating sludge . Biochar . Iron sulfide . Hazardous waste

Introduction Several technologies have been reported for the treatment of electroplating sludge (ES), including acid/surfactant leaching (Li et al. 2010a), recovery of valuable metals (Huang et al. 2013), immobilization of heavy metals by fixatives (Asavapisit et al. 2005; Bednarik et al. 2005; Kuchar et al. 2006; Pileckaite et al. 2015), and biological methods (Prabhu and Baskar 2015a, b; Shi et al. 2008) (Table 1). Previous studies showed that acid/surfactants leaching generates by-products such as spent acid solution and heavy-metal contaminated wastewater, which may cause serious secondary pollution (Huang et al. 2013). Recovery procedure usually needs high energy consumption and operation costs (Yang et al. 2014). Biological methods are time-consuming and confronted with the issues such as how to culture highly adaptable and stable bacteria (Prabhu and Baskar 2015a; Shi et al. 2008). Among these treatment methods, immobilization with the addition of fixatives is considered to be an effective way with respect to the ease of operation, fast reaction rate, as well as high immobilization efficiency. Fixatives can reduce the leachability of heavy metals through adsorption, ionic exchange, and chemical precipitation (USEPA 1982). However, traditional fixatives, such as

Immobilization of heavy metals by fixatives

Immobilization of heavy metals by fixatives

An electroplating wastewater treatment plant in Zhejiang

Sludge B and sludge I: A chromate conversion coating process; Sludge K: A galvanic electroplating process

A galvanizing plant

Huizhou Hazardous Waste Management Center in Guangdong province of China A Ni-Cu electroplating factory in southern Taiwan Simulated zinc plating sludge

Leaching

Recovery of valuable metals

Sources of ES Dosage

Experimental conditions pH

12–13

Na2S-to-Zn2+ molar ratio = 1.5:1

Na2S

FeS and BC

FeS-to-ES mass ratio = 1:5 BC-to-ES mass ratio = 1:2

8.3

First step: Asphalt-to- 11–13 Asphalt emulsions emulsifier-to(50 %-55 % and stabilizer-to-sludge 60 %), emulsifiermass alkalized vinsol resin ratio = 40:3:5:200 and salts of higher saturated organic acid Second step: Asphaltto-sludge mass stabilizer-bentonite ration = 1:20 Clay and kaolin Sludge B and I: Clay- – kaolin-sludge mass ratio = 85:10:5 Sludge K: Clay-tosludge mass ratio = 95:5

–

Additive-to-sludge mass ratio = 1:5

Limestone-to-cullet mass ratio = 4:6

Proper amount 98 % 1.5–3.2 First-stage: Sulfuric sulfuric acid-toacid, 30 % hydrogen 20 mL 30 % hyperoxide, and drogen peroxide-toultrasonic 200 g sludge enhancement Second-stage: Ultrasonic agitation

Method/Chemicals

Reported ES treatment technologies

Treatment technology

Table 1

–

–

Filtration

Gravity

Filtration

FeS: – 5 BC: 3

0.17

Sludge B and I: 10751100 Sludge K: 1000-1050

25

5

2

–

37–44

–

–

1450

–

Temperature (°C)

Sludge B and I: Distilled water (pH = 6) leachability was declined by 32.5 − 79.3 % for Cr Sludge K: Distilled water (pH = 6) leachability was declined by 94.2 % for Cr FeS: TCLP-based leachability was declined by 59.6, 100, 63.8, 73.5,

(Bednarik et al. 2005)

(Kuchar et al. 2006)

(Huang et al. 2013)

(Li et al. 2010a)

References

FeS: 768 BC: 500

This work

Sludge B and I: 1750 (Pileckaite et al. Sludge K: 840 2015)

Concentration of Zn 1250 in supernatant was declined by 80.9 % TCLP-based 935 leachability was declined by 95.0 % for Cd, Cr, Ni, Zn, Cu, and Fe

Concentration of Cu 576 and Ni in digestion solution was >95.0 %

97.4, 98.5, 98.6, 3000 98.3, and 100 % leaching efficiencies of Cu, Ni, Zn, Cr and Fe

Economic Costs (CNY/t) (without Time Separation Experimental results considering the operational (d) method expenses)

Environ Sci Pollut Res

Biological method

Biological method

Treatment technology

Method/Chemicals

The sedimentation Thiobacillus tanks at an ferrooxidans-toelectroplating thiobacillus factory in thiooxidans Guangzhou, concentration China ratio = 1:1 The treatment Acidithiobacillus plant of ferrooxidans Electroplating Industry, Chennai, India The treatment Acidithiobacillus plant of ferrooxidans and Electroplating sulfur Industry, Chennai, India

province, China.

Sources of ES

Table 1 (continued)

Bacterial medium with 2.8 1 % (w/v) sludge, and 6 g/L sulfur 28

28

Bacterial medium with 1.3 1 % (w/v) sludge

Temperature (°C)

30

pH

2.0

Bacteria-to-sludge concentration ratio = 99.9:0.1

Dosage

Experimental conditions

20

20

7

Filtration

Filtration

–

Supernatant:98.0 % / removal of Zn, 82.3 % removal of Ni, and 71.8 % removal of Cr

and 90.5 % for Cr (TCr), Cu(II), Ni(II), Pb(II), and Zn(II). BC: TCLP-based leachability was declined by 35.1, 30.6, 22.3, 23.1, and 22.4 %, respectively. Supernatant: No / removal of Cr was observed, 70.3 % removal of Ni, and 100 % removal of Cu. Supernatant: 96.3 % / removal of Zn and 84.4 % removal of Ni

Economic Costs (CNY/t) (without Time Separation Experimental results considering the operational (d) method expenses)

(Prabhu and Baskar 2015b)

(Prabhu and Baskar 2015a)

(Shi et al. 2008)

References



ceramic (Pileckaite et al. 2015), calcium oxide (Mallampati et al. 2012), polyfluoroalkoxy (PFA) (Asavapisit and Chotklang 2004), cement, pulverized fuel ash (Asavapisit et al. 2005), asphalt emulsion (Bednarik et al. 2005), and Na2S (Liang 2012), are costly and harmful to the environment. Hence, environmental friendly and cost-effective fixatives with high immobilization efficiency of heavy metals are urgently needed for the treatment of ES to ensure safe landfill disposal. Biochar (BC) is a black carbon produced during the pyrolysis of organic wastes (such as straw and feces) (Kim et al. 2015). When applied to the environment, BC can immobilize heavy metals, sequestrate carbon from atmosphere, and enhance soil fertility. BC is very effective in immobilizing heavy metals such as Cu(II), Pb(II), Cd(II) (Wang et al. 2015), Cr(III), Cr(VI) (Agrafioti et al. 2014), As(V) (Hu et al. 2015), and Hg(II) (Gomez-Eyles et al. 2013) in water and soil due to its porous morphology, high surface area, and abundant oxygen-containing groups (Puga et al. 2015; Tang et al. 2013; Tran et al. 2015). However, most of these studies have focused on the remediation of heavy metals in lab-simulated wastewater and/or soil/ES. Inorganic sulfides are effective fixatives for the removal of heavy metals with low solubility of metal sulfide (Egirani et al. 2014a, b; Kuchar et al. 2007). For example, Kuchar et al. (2007) reported that more than 79.0 % of Zn(II), Cu(II), and Pb(II) in fly ashes were immobilized with the addition of Na2S after 30 min. ZnS exhibited an As(III) sorption capacity of 7.8 to 8.5 μg/g with increasing pH from 4 to 8 (Egirani et al. 2014b). FeS is a natural sulfide mineral and an excellent fixative for heavy metals for its unique molecular structure, compositions, and surface chemical properties (Han et al. 2014; Henderson and Demond 2013; Lu et al. 2006). Heavy metals can be immobilized by FeS through adsorption, ion exchange, and/or chemical precipitation of highly insoluble metal sulfides (Liu et al. 2008). Numerous studies have reported on the remediation of heavy-metal contaminated water prepared in laboratory by FeS (Gong et al. 2016; Han et al. 2015; Liu et al. 2008), but in-depth studies of industrial application such as ES are rare. The overall objective of this study is to investigate the immobilization effectiveness and mechanisms of heavy metals in ES by BC and FeS, respectively. The main advantage of this process is that the environmental friendly and cost-effective BC and FeS can be advantageous to immobilize heavy metals in the ES to ensure safe landfill disposal. The effects of treatment time and fixative dosage on the immobilization effectiveness are evaluated, and the properties of BC and FeS are examined to acquire further insights into the underlying immobilization mechanisms. Furthermore, the treatment costs of ES using BC and FeS are evaluated.

Materials and methods Materials ES was collected from an electroplating wastewater treatment plant in Zhejiang province, China. The pristine ES was placed in sealed polyethylene plastic bags and stored in a fridge at 4 °C. Before use, the sample was air-dried for 5 days, sieved through a 2-mm screen, and mixed thoroughly. Heavy metal content in the ES was determined per the US Environmental Protection Agency (EPA) method 3050B (1996). Wheat straw obtained from Shandong province of China was air-dried for 7 days and milled into powders of ~2 mm as the feedstock biomass for BC production. All chemicals used in this study were of analytical grade. Sodium sulfide nonahydrate (Na2S · 9H2O) and iron sulfate heptahydrate (FeSO 4 · 7H 2 O) were purchased from Fengchuan Chemical Techology Co., Ltd. (Tianjin, China). Preparation of BC and FeS BC was prepared following a revised method by Yan et al. (2014). In brief, 10-g wheat straw powders were pyrolyzed in a porcelain crucible under the oxygen-limited conditions at 600 °C for 2 h in a muffle furnace (SX-G07102, Zhonghuan Experimental Furnace Co., Ltd., Tianjin, China). The resultant product was treated with 500 mL of 1 mol/L HCl solution for 24 h to remove minerals and washed with DI water until the pH reached neutral. Finally, the samples were oven-dried at 80 °C for 24 h and stored in glass vials for further use (Yan et al. 2014). FeS was prepared through co-precipitation of Na2S · 9H2O and FeSO4 · 7H2O in the aqueous phase under anoxic conditions (Equation (1)): FeSO4 þ N a2 S→ FeS ðsÞ þ N a2 SO4

ð1Þ

Characterization of BC and FeS Scanning electron microscopy (SEM) (Shimadzu SS-550, Shimadzu Corp., Kyoto, Japan) was carried out to observe the structures and surface morphology of the fixatives. The UV-vis absorption spectra were obtained using a UV-visible spectrophotometer (Shimadzu UV-3600, Shimadzu Corp., Kyoto, Japan) in the wavelength range of 200–900 nm. The surface functional groups were observed by fourier transform infrared spectroscopy (FTIR) (FTS6000, Bio-rad, Beijing, China). The crystalline compositions were identified by Xray diffraction (XRD) using a Bruker D8 FOCUS diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) with a Cu Kα radiation (λ = 1.5406 Å) at a scan speed of 4°/min and a step size of 0.02° in the 2θ range of 3–80°. The thermal stability of the samples was tested by thermal gravimetric analysis (TGA)


(TG209, Netzsch, Shanghai, China). The specific surface area, pore size, and pore volume of BC and FeS were determined by the BET adsorption method (ASAP2460, Micromeritics, Atlanta, USA). Zeta potential (ζ) was determined using a Malvern Zeta sizer Nano Instrument (ZEN3690, Malvern Instruments, Worcestershire, UK). Surface elemental compositions of the ES before and after immobilization by BC or FeS were analyzed by X-ray photoelectron spectroscopy (XPS) (PHI-5000, ULVAC-PHI, Chigasaki, Japan). Immobilization of heavy metals in ES by BC and FeS Effects of treatment time on immobilization efficiency Batch experiments were conducted to evaluate the effects of contact time on the immobilization ability of BC and FeS. For BC, 500 mg of BC was mixed with 1000 mg ES in 40-mL glass vials, resulting in a BC-to-ES mass ratio of 1:2. 2 mL of DI water was added to the mixture. The vials were then sealed and placed on an end-over-end rotator (WH-963, Hualida Laboratory Equipment Co., Ltd., Jiangsu, China) at 40 rpm at 25 °C. The immobilization of heavy metals was followed for 5 days by carrying out toxicity characteristic leaching procedure (TCLP) tests. For FeS, 400 mg FeS was mixed with 2000-mg ES in 4 mL water in 40-mL glass vials, resulting in a FeS-to-ES mass ratio of 1:5. TCLP-leachable heavy metals were followed for 3 days. For all experiments, pH of the mixtures was measured before and after the reaction. At predetermined times, a small portion of the mixture was collected to determine the moisture content. TCLP tests were performed to evaluate the leachability of heavy metals in the untreated and BC- or FeS-treated ES following the Environmental Protection Industry Standards of People’s Republic of China (HJ/T300-2007). In brief, 1 g of the airdried sample was mixed with the TCLP extraction solution at a solid-to-liquid ratio of 1 g: 20 mL. The mixture was placed on an end-over-end rotator at 30 rpm for 18 h and then allowed to settle by gravity for 30 min. The supernatant was filtered by 0.45-μm mixed cellulose ester filter membrane, and the filtrate was analyzed for aqueous heavy metal concentration. Control tests were conducted in the absence of fixatives under otherwise identical conditions. The results showed that the coefficient of variation (cv) of control samples in each batch experiment is