沙漠研究 19-1, 233- 236 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Influence of Tailing pH on the Sorption of Copper by Sulphide Mine Tailing
Antoine KARAM1, Lotfi KHIARI1, Alfred JAOUICH2
Abstract: A laboratory experiment was conducted to evaluate the retention of copper (Cu) bysulphide mine tailings previously treated with lime (calcium carbonate) and submerged withwater over 10 years. Sub-samples of air-dried mine tailings (pHtailing range: 2.56 to 7.60) wereequilibrated with 30 mL of 0.01 M CaCl2 containing 100 mg Cu L-1, as CuSO4.5H2O, for sevendays at room temperature. Afterwards, they were centrifuged and filtered. The filtrates wereanalyzed for Cu, by atomic absorption spectrophotometer, and pH (pHequilibrium). The amountof Cu retained by mine tailing solids was calculated based on the difference between the initialand equilibrium Cu concentrations. The sorption experiment was replicated two times. Afterthe sorption step, extractable acid-soluble Cu in tailing samples was assessed by extraction with
Mehlich-3 solution. Results indicated a significant positive effect of lime application rate on
Cu sorption. The sorption coefficient was positively correlated (p<0.001) with bothpHequilibrium and pHtailing. In general, desorption showed that the Cu sorption was not rigidly
bound under acidic conditions. The percentage of Cu released in the tailings without lime wasmuch more than that released in the limed tailings. A positive linear relationship was foundbetween the amounts of Cu desorbed and the amounts of Cu previously adsorbed. Copper inmine tailings may leach into water, especially under acidic conditions. The results highlightthe importance of maintaining neutral pH conditions in sulphide mine tailings in order toprotect surface water from the hazards of soluble anthropogenic Cu.
Keywords: Acid mine drainage, Desorption, Liming

1. Introduction
Acid mine drainage (AMD), also called acid rock drainage (ARD) is a worldwide environmental
problem facing the mining industry (Marcoux and Grenier, 1990). Despite the fact that it is a natural
occurrence resulting from the exposure of sulphide minerals to atmospheric agents such as air and water,
AMD can cause considerable damage to the environment. Acid mine drainage can contain elevatedconcentration of leachable trace metals (Lapakko, 2002).
The lixiviation of copper (Cu) from strongly acidic sulphide mine tailings in arid and temperateregions represents an environmental risk because of the potential adverse effects it may pose to ground andsurface water around mines. However, bonding of Cu to mine tailings can limit transfer to surrounding
water. Liming is known to be effective in enhancing Cu sorption by adsorption and precipitation, andconsequently reducing Cu mobility in Cu-polluted soils (Singh and Oste, 2001). Rodriguez-Rubio et al.
(2003) suggested that the mobility of Cu in a calcareous soil is likely to be increased when calcium
carbonate (CaCO3) is removed. Thus, the sorption of anthropogenic soluble Cu by submerged-sulphidemine tailings is of great environmental concern. A laboratory sorption experiment was undertaken toassess the sorption of Cu by sulphide mine tailings that have been limed and maintained under water
saturation during 10 years in order to prevent the oxidation of tailings (Samad and Yanful, 2005).
2. Materials and Methods
The sulphide mine tailings used originated from the Solbec site at Thetford-Mines in the province ofQuebec (Canada). The original Cu-Zn-Pb ore body consisting of pyrite, chalcopyrite, sphalerite, galena
and pyrrhotite, has been exploited from 1962 to 1970 producing 1.9Mt of ore. Solbec mine tailings havea 100 μm median grain-size and a rate of 20% sulphide and 2-5% heavy metal (Marcoux and Grenier,1990). An incubation experiment was carried out 1994 in triplicate on oxidized and composite samples
placed in plastic pots. The treatments consisted of three limestone levels (2, 4 and 8 g CaCO3/ 400 g oftailing, representing approximately 0.5, 1 and 2%, respectively) and a control (without lime). The pots
1

Department of Soils and Agrifood Engineering. Laval University, Quebec, QC G1V 0A6, Canada. Fax no.:418-6563723, Tel. no.: 418-6567420, E-mail: Antoine.Karam@fsaa.ulaval.ca;
2
Department of Earth and Atmospheric Sciences, University of Quebec at Montreal, Montreal, QC H2C 3P8, Canada.

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were packed with 40 mm tailing depth. The lime was incorporated into 0-20 mm and 0-40 mm depth.
The tailings were covered with 80 mm of deionized water and then incubated under saturated conditions atroom temperature for 10 y in order to prevent their oxidation (De Coninck and Karam, 2006). Afterincubation, sub-samples were air-dried, ground and passed through a 2-mm sieve.
One gram of air-dried tailings (pHtailing range: 2.56 to 7.60) was equilibrated with 30 mL of 0.01 M
CaCl2 containing 100 mg Cu L-1, as CuSO4.5H2O, for seven days at room temperature (22 ˚C). The
suspensions were then centrifuged at 2000 rpm for 5 minutes and the supernatant solutions were filteredthrough Whitman No. 42 filter papers. The pH values of the filtrates (pHequilibrium) were measured and theconcentrations of soluble Cu in the filtrates were determined by atomic absorption spectrophotometer.
The amount of Cu adsorbed was calculated as the difference between Cu added and Cu remaining insolution. The sorption coefficient (Ks) was used to interpret the sorption data: Ks = Q/C, where Q is theamount of Cu adsorbed (mg kg-1), and C is Cu concentration in the equilibrium solution (mg L-1). The
sorption experiment was replicated two times.
After the sorption step, extractable acid-soluble Cu in tailing samples was assessed by extraction withMehlich-3 solution. Mehlich-3 solution (Mehlich, 1984), which is composed of 0.2 M CH3COOH, 0.25
M NH4NO3, 0.015 M NH4F, 0.013 M HNO3 and 0.001 M ethylene diamine tetraacetic acid, has beenreported to extract occluded Cu binding sites, organically bound Cu fraction, and soluble, exchangeable
and specifically adsorbed Cu fractions (Reed et al., 1993).
3. Results and Discussion
Adsorbed Cu and Ks values increased with increasing lime rate (Table 1). However, the t-test(p<0.05) did not reveal significant difference between the control (no lime) and the lowest rate of lime
(0.5%). The values of Ks ranged from 0.2 (without lime) to 345.0 L kg-1 (highest lime rate). Minetailings without lime (pH 2.56) adsorbed 0.5% of added Cu whereas lime-amended tailings (pH 2.72 to7.60) can adsorb from 1.0 (lowest lime rate) to 92.0 % (highest lime rate) of added Cu. This observationsuggests that the more submerged-tailing is neutral to slightly alkaline, the more it will remove
anthropogenic Cu from the surface water. Residual CaCO3 present in the mine tailing matrix may act as asorbent (Papadopoulos and Rowell, 1989), retaining Cu through ion exchange (Cavallaro and McBride,1978). Ks values were positively correlated (p<0.001) with both pHequilibrium (r=0.800) and pHtailing(r=0.698). Similar positive correlation between Cu adsorption and pH has been reported by Jarvis (1981).
This result is in agreement with literatures, where the amount of Cu adsorbed by soils, clays and sediments
increased with pH (Yuan et al., 2007; Zhang and Zheng, 2007; Arias, 2005; Phillips et al., 2004; Hue et al.,
1997; Harter, 1983; Maguire et al., 1981). The relationships between Cu adsorbed and both pHequilibrium
and pHtailing are better described by a quadratic equation (Fig. 1). The differences in Cu sorption between
mine tailing samples could be attributed to the pHtailing induced by previous CaCO3 application. The
higher content of residual lime in the tailing sample and the more sites there are for Cu sorption. Basedon evidence from many experiments, Cu has very low solubility in alkaline and calcareous soils (McBrideand Bouldin, 1984; Jarvis and Jones, 1980; Cavallaro and McBride, 1978). Residual CaCO3 surfaces
present in sulphide mine tailings act also as nucleation sites for precipitating Cu (McBride, 2000). Thus,
stabilization of sulphide mine tailings using lime would transform such waste into a matrix with metal
sorption properties. Davies et al. (1999) who studied the efficacy of lime amendment to geochemicallystabilize mine tailings, found that liming facilitates alteration of pyrite to ferrihydrite that sequestered
Table 1. Average values of pHtailing, amount of Cu adsorbed, Ks, pHsuspension and amount of extractableacid-soluble Cu (desorbed Cu).

CaCO3 rate
(%)
00.5
1.0
2.0

pHtailing

Adsorbed Cu
-1

2.68
2.79
4.10
6.25

(mg kg )67.50
110.63247.501653.80

Ks

pHsuspension

Desorbed Cu

2.83
2.73
3.62
4.82

(mg kg-1)
37.20
30.37
63.37
1174.90-1(L kg )
0.70
1.152.73103.60

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3500
y = 192.3x 2 - 952.7x + 1243
R2 = 0.941

Adsorbed Cu, mg/kg

3000
2500
2000
1500
1000
500
0234567pH suspension

Fig. 1. Relationship between the pH of the equilibrium solution and theamount of Cu adsorbed by limed tailings.

weight percent concentrations of As, Cu, Pb, and Zn.
In terms of the quantities initially adsorbed, the percentage of desorbed Cu was very high for tailings
without lime (96%) compared to the limed tailings (16-84%). The desorption process was also found todepend on the pH of the solution. A decrease in pH will cause desorption of the Cu initially adsorbed on
the tailing. According to Van Tichelen et al. (2001), adsorbed Cu could easily be desorbed by protons.
A positive linear relationship was found between the amounts of extractable acid-soluble Cu and theamounts of Cu previously adsorbed (r=0.983, p<0.001). This result indicates that under acidic conditions,adsorbed Cu is readily and largely desorbed. The environmental consequence of this observation isimportant. Under potential reacidification of neutralized mined lakes, much of anthropogenic Cu initiallyadsorbed by the tailing will be released back into the surface water.
4. Conclusions
Copper sorption by limed sulphide mine tailings is highly correlated with pH. Heavily limed tailings
show high Cu sorption coefficient. Consequently, sulphide mine tailings could adsorb significant
quantities of Cu from contaminated water and surrounding environment, depending upon pH conditions.
The results highlight the importance of maintaining neutral pH conditions in submerged sulphide minetailings in order to protect surface water from the hazards of soluble anthropogenic Cu.
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