Removal of Cd, Cu, Pb and Zn from Aqueous Solutions by Biochars

SUPPLEMENTARY MATERIAL

Removal of Cd, Cu, Pb and Zn from aqueous solutions by biochars

Doumer, M.E.a, Rigol, A.b, Vidal, M.b, Mangrich, A.S.a aDepartment of Chemistry, Federal University of Paraná - UFPR, 81531-990 Curitiba, PR, Brazil bDepartment of Analytical Chemistry, University of Barcelona, Martí i Franquès 1-11, 08028-

Barcelona, Spain

Materials and Methods

Biomasses and pyrolysis conditions

Sugarcane bagasse (SB), a waste material derived from the production of sugar and ethanol, was supplied by the sugar company Melhoramentos S.A. (Paraná State, Brazil). Eucalyptus forest residues (CE), consisting of brushwood mixed with eucalyptus biomass (Eucalyptus grandis and

Eucalyptus saligna), was supplied by the company Granfor (Rio Grande do Sul State, Brazil).

Castor meal (CM) was derived from the process of production of bio-oil from castor beans (Ricinus communis L.). After extraction of the oil from the seed of the castor bean, the resulting castor bean cake was subjected to solvent extraction, generating castor meal as a byproduct, which also contained some portion of capsule husks of castor oil seeds. Green pericarp of coconut (PC)

(Cocos nucifera) accumulates on beaches and in other public spaces where natural coconut water is consumed. The material used in this study was from Bahia State, Brazil. Water hyacinth (WH)

(Eichornia crassipes) was collected from ponds in Sergipe State, Brazil.

The process of pyrolysis is described in a previous work (Doumer et al., 2015). In short, biomass samples were dried at room temperature, and some of them (CE and PC) were crushed to fit in the reactor. The pyrolysis experiments were performed using a 2 L internal volume borosilicate reactor

(internal diameter 15 cm, height 34 cm) externally heated by an electric furnace equipped with temperature control. The weight of biomass used in each batch of pyrolysis depended on its density. After conditioning the biomass, the reactor was closed in order to obtain an oxygen-limited atmosphere, except for an exit for gases that were transferred through a water condenser at 20 °C 1 in order to separate the condensable fraction (bio-oil) and the non-condensable gases. The temperature was raised from room temperature to 350 °C at a rate of approximately 5 °C min-1 giving a maximum time of 70 min in the reactor. The CM and WH biomasses were maintained in the furnace for additional 30 min at 350 °C to complete the pyrolysis. The biochars were then removed from the reactor after cooling the system to room temperature. The percentage yields of biochar were 40.7±2.1% (CE), 74.1±6.4% (CM), 47.0±3.9% (PC), 41.2±1.1% (SB), and 56.9±2.1%

(WH) (Doumer et al., 2015). Except for WH, whose biomass had an original particle size < 0.85 mm, the rest of biochars were ground and sieved through a 2 mm mesh, and then stored prior to analyses.

Biochar characterization

The moisture contents of the materials were determined by drying aliquots at 105 ºC. Loss on ignition (LOI) was determined from the loss of weight after heating at 450 ºC for 4 h. The pH was measured in water and 1 M KCl solution, using a 1:10 (solid/liquid) ratio. The pH value at the point of zero charge (PZC) was estimated as follows: PZC = 2 x pH (in KCl) - pH (in water) (Zelazny et al. 1996). The cation exchange capacity (CEC) was determined using the sodium acetate method

(Thomas 1982).

Total carbon, total nitrogen, and total organic carbon (TOC) were measured by elemental analysis

(EA-1108, CE Instruments, Thermo Fisher Scientific). TOC was determined after removal of the carbonate content with 2 mol L-1 HCl. To quantify the dissolved organic carbon content (DOC), 50 mL of MiIli-Q water were added to 2 g of the biochar. The resulting suspension was shaken end- over-end for 30 min, followed by centrifugation. The supernatant was filtered, acidified to pH 2, and the DOC concentration was determined using a total organic carbon analyzer (TOC-5000,

Shimadzu).

The humic and fulvic acid contents (HA and FA, respectively) were determined by an official method (BOE 1991) based on an extraction at alkaline pH to dissolve the acids, followed by determination of total organic carbon in the extract. An aliquot of the extract was acidified to pH 1 in order to precipitate the HA, which was then separated and dissolved in an alkaline medium. 2 Finally, the total carbon content associated with the HA was determined in the resulting supernatant. The FA content was calculated as the difference between the total organic carbon in the initial extract and the carbon in the HA extract.

The neutralization capacity of the samples was determined with a pH titration test (CEN/TS 2006).

First, the initial pH of each sample (2 g) was measured in deionized water (200 mL). The pH of the suspension was then measured after consecutive additions of 100 µL of HNO3 or NaOH, with 20 min of stirring after each addition. The acid and base additions were repeated until the pH 2-12 range had been covered. This test also enabled determination of the acid neutralization capacity

(ANC) of the materials, defined as the quantity of acid or base (meq kg-1) required to shift the initial pH to a pH of 4. Therefore, for those materials with an initial pH higher than 4, the ANC measurement provided an estimation of the buffering capacity with respect to external acidic stresses.

Ash analysis of the biochar samples was conducted according to the ASTM protocol D1762-84

(ASTM 2013). Solid-state 13C NMR data were obtained at a resonance frequency of 100.6 MHz using an Inova 400 spectrometer (Varian, Palo Alto, CA, USA). The total contents of major and trace elements were determined using a modification of U.S. EPA Method 3052 (U.S.EPA 1996), based on microwave digestion with a mixture of acids. A 0.3 g portion of sample was weighed in a closed PTFE vessel, and 6 mL of 69% HNO3, 2 mL of 40% HF, and 1.5 mL of 30% H2O2 were added in the first step. The temperature was gradually increased to 190 ºC over 15 min, followed by a dwell time of 30 min. In the second step, 16 mL of 5% H 3BO3 was added to redissolve the fluoride precipitates, and the same temperature program was applied. After cooling the extracts to room temperature, they were diluted with Milli-Q water to a final volume of 50 mL and stored at 4

ºC prior to analysis.

3 Oxidizing digestion of the supernatants

Aliquots (10 mL) of the solutions were mixed with 1 mL of H2O2 and 2 mL of HNO3 and digested using the following procedure: 10 min at 90 °C, a dwell time of 5 min, 10 min at 120 °C, 10 min at

190 °C, and a final dwell time of 10 min at 190 oC (Silva and Ciminelli 2009).

Determination of major and trace elements in the solutions

The major and trace elements were determined in the water extract solution and from sorption- desorption experiments using a Perkin-Elmer Model OPTIMA 3200RL ICP-OES equipped with a

Perkin-Elmer AS-90 Plus autosampler. This equipment consists of a radiofrequency source

(working at 1150 W and a frequency of 40 MHz), a cross-flow nebulizer, and an SCD (segmented- array charge coupled device) detector. The following emission lines (nm) were used for each element determined: Cd, 214.440 and 228.802; Cu, 324.752 and 327.393; Pb, 220.353; Zn,

206.200 and 213.857; Ca, 315.887 and 317.933; Mg, 279.077 and 285.213; K, 766.490; Na,

330.237; As, 188.979 and 193.696; and Ni, 231.604. The detection limits of the inductively coupled plasma optical emission spectroscopy (ICP-OES) were 0.01 mg L-1 for Cd and Cu; 0.025 mg L-1 for

Zn; 0.1 mg L-1 for Ca, Mg, and Ni; 0.2 mg L-1 for Pb; 0.5 mg L-1 for As; and 1 mg L-1 for K.

A Perkin-Elmer ELAN 6000 inductively coupled plasma mass spectrometer (ICP-MS), equipped with a PerkinElmer AS-91 autosampler, was used for the lowest trace element concentrations.

Several element isotopes (111Cd, 112Cd, and 114Cd; 63Cu and 65Cu; 208Pb; 66Zn, 67Zn, and 68Zn; 75As; and 60Ni and 62Ni) were measured to detect and control for possible isobaric or polyatomic interferences. To correct for instabilities in the ICP-MS measurements, 103Rh was used as an internal standard with a concentration of 200 µg L-1 in all of the samples. The detection limits of the

ICP-MS measurements were 0.02 μg L-1 for Cd, 0.05 μg L-1 for Pb, 0.1 μg L-1 for Cu, and 0.2 μg L-1 for As, Ni, and Zn.

4 Table S1. Relative distribution (%) of organic carbon in the biochars.

Aliphatica Carbohydratea Aromatica Phenolica Carboxylica Carbonyla (140–165 (0–48 ppm) (50–100 ppm) (100–140 ppm) ppm) (165–190 ppm) (190–220 ppm) CE 22.3 11.3 43.5 16.8 3.4 2.7 CM 34.4 19.2 25.0 11.6 7.6 2.1 PC 23.9 8.4 45.5 16.4 3.1 2.7 SB 23.9 9.1 45.3 15.5 3.2 3.0 WH 31.3 10.7 30.7 15.6 7.9 3.7 a Solid-state 13C CP-MAS NMR spectra were acquired using a Varian Inova 400 spectrometer (Varian, Palo Alto, CA, USA). The realtive distribution of the organic carbon groups was determined by integration of the respective areas in the NMR spectra (Tsang et al., 2013).

5 Table S2. Kd and R% for Cd, Cu, Pb, and Zn, calculated from data reported in the literature.

Biochar material Metal Ci Kd R (%) Reference (mmol L-1) (L kg-1) Cd 5 189 48.6 Dairy manure char Cu 5 853 81.0 (Xu et al., 2013a) Zn 5 188 48.5 Peanut straw char Cu 15 368 74.7 Soybean straw char Cu 15 99 44.3 (Tong et al., 2011) Canola straw char Cu 15 57 31.5 Activated carbon Cu 15 13 9.6 Cd 5 15 7.0 Cu 5 14 6.5 Rice husk biochar (Xu et al., 2013b) Pb 5 33 14.0 Zn 5 22 10.1 Digested whole sugar beet char Pb 2.9 103 17.1 (Inyang et al., 2011) Digested animal waste char Pb 2.9 79 13.6 Cd 0.35 40 3.8 Alamo switchgrass Cu 0.63 111 10.0 (Regmi et al., 2012) Cd 0.35 40 3.8 Activated carbon - coconut coir Cu 0.63 47 4.5 Cd 0.9 7530 99.7 Cu 1.6 22761 99.9 Chitosan Pb 0.5 205211 100.0 Zn 1.5 39576 99.9 Cd 0.9 47 70.1 Cu 1.6 1814 98.9 Egg shell Pb 0.5 6429 99.7 Zn 1.5 475 96.0 (Shaheen et al., 2013) Cd 0.9 770 97.5 Cu 1.6 127 86.4 Potassium humate Pb 0.5 2020 99.0 Zn 1.5 54 72.9 Cd 0.9 2510 99.2 Cu 1.6 4316 99.5 Sugar beet factory lime Pb 0.5 35688 99.9 Zn 1.5 4338 99.5

6 -1 Table S3. Cations release following Cd, Cu, Pb, and Zn sorption onto the biochars, for Ci of 0.1, 1, and 5 mmol L . Z Control Cd Cu Pb n 0 a Ci 0 0.1 1 5 0.1 1 5 0.1 1 5 . 1 5 1

CE Csorb - 2 24 116 2 23 117 2 24 119 2 23 116 3 Ca+Mg 22 29 37 48 32 44 116 39 38 100 37 58 0 4 K 32 46 48 58 47 53 68 50 50 63 49 61 7 6 pH 7.2 6.8 6.6 6.4 6.8 6.6 5.5 6.2 5.6 5.4 . 6.0 6.1 3

CM Csorb - 2 24 117 2 23 120 2 24 125 2 24 119 5 Ca+Mg 42 51 62 90 56 67 113 51 59 105 62 93 2 1 K 118 137 140 148 141 143 164 139 135 157 3 136 144 3 6 pH 7.3 7.3 6.9 5.8 6.9 6.3 5.0 6.9 7.3 5.1 . 5.9 5.7 1

PC Csorb - 2 24 118 2 24 122 2 24 122 2 24 120 Ca+Mg 4 5 8 18 3 6 19 7 7 21 4 7 23 3 K 252 307 310 344 290 322 405 298 323 386 0 305 363 6

7 7 pH 8.9 7.8 7.6 6.9 7.8 7.5 6.1 8.1 7.6 6.1 . 7.1 6.8 6

SB Csorb - 2 24 118 2 24 114 2 24 115 2 23 114 1 Ca+Mg 10 12 20 21 13 26 26 15 25 26 21 24 3 2 K 17 25 24 30 26 30 33 29 28 32 27 30 5 6 pH 6.0 5.9 5.7 5.5 6.4 5.4 4.5 6.6 5.0 4.4 . 5.8 5.3 2

WH Csorb - 2 25 123 2 24 123 2 25 124 2 25 122 2 Ca+Mg 266 263 271 343 283 287 377 269 264 357 6 261 333 4 1 6 K 1570 1683 1545 1523 - 1540 1500 1566 1552 1510 1529 1489 4 0 8 pH 9.2 8.6 8.5 7.5 8.2 8.2 7.5 8.3 8.3 7.7 . 8.2 7.5 2 a -1 Csorb, Ca+Mg, and K in mmol kg .

8 Table S4. Ranges of values of desorption parameters of the examined metal-biochar -1 combinations (Kd,des, L kg ; Rdes, %).

Metal CE CM PC SB WH

6 6 6 Cd Kd,des,min 114190 >10 >10 391460 >10

6 6 6 6 6 Kd,des,max >10 >10 >10 >10 >10

Rdes,min 1.1 0.1 0.4 0.6 0.2

Rdes,max 10.1 0.7 1.2 3.0 0.9

6 6 6 Cu Kd,des,min 209590 >10 261840 >10 >10

6 6 6 Kd,des,max 831250 >10 747570 >10 >10

Rdes,min 1.5 1.9 0.8 1.6 0.7

Rdes,max 5.5 5.3 2.9 6.1 1.1

Pb Kd,des,min 181620 402450 825785 360595 233550

6 6 6 Kd,des,max 396670 >10 >10 >10 438755

Rdes,min 0.1 0.1 0.2 0.1 0.2

Rdes,max 7.5 7.9 10.7 10.4 14.2

6 Zn Kd,des,min 75620 >10 551810 466980 501390

6 6 6 6 Kd,des,max 360370 >10 >10 >10 >10

Rdes,min 0.8 0.9 0.3 4.7 0.1

Rdes,max 5.3 2.6 2.8 19.3 3.7

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