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The effects of inorganic cations (Li+, K+, Mg2+, Ca2+, Ni2+ and Fe3+) and anions ( and ) that could interfere in the adsorption of TC onto the Zn-AC were investigated using batch adsorption experiments, and the results are shown in Figure 7. The concentration of anions such as and and most of cations such as Li+, K+, Mg2+, Ca2+, Ni2+ and Fe3+ in surface water is usually less than 1 mM, as reported in the literature (Hem 1985); therefore, 1 mM salts of these anions and cations were used to evaluate their effects on TC adsorption. We used the ANOVA test to compare the adsorption of TC in the presence of the anions and cations with TC adsorption in the absence of the tested anions and cations (sample containing only the adsorbent and 100 mg L−1 TC). The ANOVA test results (Table 5) indicated that all tested anions and cations affected and decreased TC adsorption (p<0.05). It should be noted that the presence of Fe3+ and Ni2+ decreases TC adsorption significantly, so that the removal percentage decreases from 96.9% to 70.1% for Fe3+ ion and from 96.9% to 74.8% for Ni2+ ion (Figure 7). The decrease in the adsorption of TC due to the presence of other anions and cations is less than 10% (Figure 7); the decrease in the adsorption of TC in the presence of anions and cations could be considered as a competition between the ions and TC species to adsorb on active sites of the adsorbent. The higher decrease in the adsorption of TC onto the Zn-AC due to the presence of Fe3+ and Ni2+ may be attributed to the highest tendency of Fe3+ and Ni2+ to adhere to the negatively charged Zn-AC, which in turn reduces ion interaction sites (or available sites) on the surface of the Zn-AC for TC adsorption. The results of this study are in good agreement with the results of the other researchers. For instance, Zhao et al. (2011b) reported that in the presence of five types of cations (Li+, Na+, K+, Ca2+, and Mg2+) the adsorption of TC on kaolinite decreased in accordance with the increase of atomic radius and valence of metal cations. They attributed the decrease in the adsorption to outer-sphere complexes formed between TC and kaolinite as well as the existence of competitor ions. Liu et al. (2012) investigated the removal of TC from water by Fe-Mn binary oxide reported that the presence of cations and anions such as Ca2+, Mg2+, CO32− and SO42− had no significant effect on the TC removal in their experimental conditions, while SiO32− and PO43− hindered the adsorption of TC. Zhao et al. (2011a) evaluated the adsorption of TC onto goethite in the presence of metal cations and humic substances. They stated that at the studied pH range, the presence of five background electrolyte cations (Li+, Na+, K+, Ca2+, and Mg2+) with a concentration of 0.01 M had little effect on the TC adsorption. The adsorption of four pharmaceuticals (carbamazepine, diclofenac, ibuprofen, and ketoprofen) to silica as a function of ionic strength, anions, cations, and natural organic matter was investigated by Bui & Choi (2010). The authors reported that the tested anions did not significantly affect the adsorption of these pharmaceuticals to silica (p > 0.05). Their results also showed that the divalent cations did not significantly affect the adsorption of carbamazepine and diclofenac; however, divalent cations at low concentrations (1 mM) increased the adsorption of ibuprofen and ketoprofen. In contrast with the present study, in that study, the presence of Fe3+ significantly increased the adsorption of the pharmaceuticals, but in our study, it significantly decreased the adsorption of TC. This difference may be ascribed to the different structure of both adsorbate and adsorbent used in the studies. Blank experiments were also run for all anions and cations at the same conditions to observe the changes in the initial concentration of TC because of possible reactions between TC and the tested anions and cations. The change in TC concentration in the blank samples was less than 2% for all cations and anions.
Table 5

Significant impact of cations and anions on the adsorption of TC onto Zn-AC

ControlBackground electrolyteSignificant impact on adsorption
TC = 100 mg L−1 FeCl3 Yes 
NiCl2 Yes 
CaCl2 Yes 
MgCl2 Yes 
KCl Yes 
LiCl Yes 
Na2SO4 Yes 
NaHCO3 Yes 
NaNO3 Yes 
ControlBackground electrolyteSignificant impact on adsorption
TC = 100 mg L−1 FeCl3 Yes 
NiCl2 Yes 
CaCl2 Yes 
MgCl2 Yes 
KCl Yes 
LiCl Yes 
Na2SO4 Yes 
NaHCO3 Yes 
NaNO3 Yes 
Figure 7

The adsorption of TC onto the Zn-AC in the presence of 1 mM cations and anions, compared to the control (initial TC 100 mg L−1). Conditions: original pH; temperature 293 K; contact time 4 h; adsorbent dosage 3 g L−1. Error bars represent the SD of two replicate experiments.

Figure 7

The adsorption of TC onto the Zn-AC in the presence of 1 mM cations and anions, compared to the control (initial TC 100 mg L−1). Conditions: original pH; temperature 293 K; contact time 4 h; adsorbent dosage 3 g L−1. Error bars represent the SD of two replicate experiments.

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