**3. Results and discussion**

#### **3.1. Effect of incubation time and pH**

Figure 1 shows the effect of the incubation time and pH on Cr (VI) removal by *L. chinensis* Sonn shell. The optimum time and pH for Cr (VI) removal are 10 min and pH 1.0, at constant values of biosorbent dosage (1 g/100 mL), initial metal concentration (100 mg /L) and temperature (28°C). The literature [11], report an optimum time of 60 min., for the removal of lead by orange waste, 30 min and 60 for the removal of Cr (VI) by the tamarind peel and eucalyptus bark [12, 16]. Changes in the permeability of unknown origin, could partly explain the differences found in the incubation time, providing greater or lesser exposure of the functional groups of the cell wall of biomass analyzed. Adsorption efficiency of Cr (VI) was observed maximum at pH 1.0 with Litchi shell. This was due to the dominant species (CrO4 2- and Cr2O7 2-) of Cr ions in solution which were expected to interact more strongly with the ligands positively charges [21]. These results are like for tamarind peel [10], but the most of authors report an optimum pH of 2.0 like tamarind seeds [10], eucalyptus bark [16], bagasse and sugarcane pulp, coconut fibers and wool, [22], for the tamarind fruit shell treated with oxalic acid [23], at pH of 2.0 and 5.0 for the mandarin bagasse [24] and almond green hull [25].

#### **3.2. Effect of temperature on Cr (VI) removal by** *L. chinensis* **Sonn shell**

Temperature is found to be a critical parameter in the bioadsorption of Cr (VI) by *L. chinensis* Sonn shell (Figure 2). The highest removal was observed at 40 and 50°C. At this point the total removal of the metal is carried out. The results are coincident for tamarind seeds with 95% of

**3.3. Effect of initial metal concentration**

**Percentage of Cr (VI) in solution**

surface of biomass [26].

rpm. 1 g biomass.

On the other hand, at low metal concentrations (100 and 200 mg/L), biomass studied, shows the best results for removal, adsorbing 100% at 10 and 20 min. respectively, while 1000 mg/L of metal is removed 100% up to 195 min of incubation at 28°C (Figure 3). Also, we observed the development of a blue-green and a white precipitate (Cr (OH)3), which changes more rapidly at higher temperatures (Figure 4). The results are coincident for tamarind peel and seeds, and *C. limonium* [10, 26, and 29]. The increase in initial concentration of Cr (VI) results in the increased uptake capacity and decreased the percentage of Cr (VI) removal. This was due to the increase in the number of ions competing for the available functions groups on the

Removal of Hexavalent Chromium from Solutions and Contaminated Sites by Different Natural Biomasses

0 20 40 60 80 100 120 140 160 180 200

100 mg/L 200 mg/L 300 mg/L 400 mg/L 500 mg/L 1000 mg/L

http://dx.doi.org/10.5772/56152

211

**Time (min)**

**Figure 3.** Effect of initial metal concentration on Chromium (VI) removal by *L. chinensis* Sonn shell. 28oC. pH 1.0, 100

The ability of the *L. chinensis* Sonn shell to decrease the initial Cr (VI) of 1.0 g/L and Cr (III) production in solution are analyzed. Figure 5 shows that the shell exhibited a remarkable efficiency to diminish Cr (VI) level with the concomitant production of Cr (III) as Cr(OH)3 in the solution (indicated by the formation of a blue-green color and a white precipitate (Cr

Thus, after 1 h of incubation, the shell biomass caused a drop in Cr (VI) from its initial concentration of 1.0 g/L to almost undetectable levels and the decrease level occurred with no significant change in total Cr content. As expected, total Cr concentration remained constant over time, in solution control. These observations indicate that Litchi shell is able to reduce Cr (VI) to Cr (III) in solution. Furthermore, as the *L. chinensis* Sonn shell contains vitamin C and

**4. Time course of Cr (VI) decrease and Cr (III) production**

(OH)3) and his determination for Cromazurol S, (Figures 4 and 6) [19, and 20].

**Figure 1.** Effect of incubation time and pH on Chromium (VI) removal by *L. chinensis* Sonn shell. 100 mg/L Cr (VI). 28oC, 100 rpm. 1 g biomass.

removal at 58°C and 3 h [26], for the adsorption of cadmium (II) from aqueous solution on natural and oxidized corncob (40°C and 5 days) [27], but this are different for the mandarin waste [24], *Caladium bicolor* (wild cocoyam) biomass [29] and *Saccharomyces cerevisiae* [30].The increase in temperature increases the rate of removal of chromium (VI) and decreases the contact time required for complete removal of the metal, to increase the redox reaction rate [26].

**Figure 2.** Effect of temperature on Chromium (VI) removal by *L. chinensis* Sonn shell. 100 mg/L Cr (VI). pH 1.0, 100 rpm. 1 g biomass.

#### **3.3. Effect of initial metal concentration**

removal at 58°C and 3 h [26], for the adsorption of cadmium (II) from aqueous solution on natural and oxidized corncob (40°C and 5 days) [27], but this are different for the mandarin waste [24], *Caladium bicolor* (wild cocoyam) biomass [29] and *Saccharomyces cerevisiae* [30].The increase in temperature increases the rate of removal of chromium (VI) and decreases the contact time required for complete removal of the metal, to increase the redox reaction rate [26].

**Figure 1.** Effect of incubation time and pH on Chromium (VI) removal by *L. chinensis* Sonn shell. 100 mg/L Cr (VI).

0 10 20 30 40 50 60 70 80 90 100

**Time (min)**

0 1 2 3 4 5 6 7 8 9 10 11 12

28°C 40°C 50°C

pH 1.0 pH 2.0 pH 3.0 pH 4.0

**Time (min)**

**Figure 2.** Effect of temperature on Chromium (VI) removal by *L. chinensis* Sonn shell. 100 mg/L Cr (VI). pH 1.0, 100

**Percentage of Cr (VI) in solution**

**Percentage of Cr (VI) in solution**

210 Applied Bioremediation - Active and Passive Approaches

28oC, 100 rpm. 1 g biomass.

rpm. 1 g biomass.

On the other hand, at low metal concentrations (100 and 200 mg/L), biomass studied, shows the best results for removal, adsorbing 100% at 10 and 20 min. respectively, while 1000 mg/L of metal is removed 100% up to 195 min of incubation at 28°C (Figure 3). Also, we observed the development of a blue-green and a white precipitate (Cr (OH)3), which changes more rapidly at higher temperatures (Figure 4). The results are coincident for tamarind peel and seeds, and *C. limonium* [10, 26, and 29]. The increase in initial concentration of Cr (VI) results in the increased uptake capacity and decreased the percentage of Cr (VI) removal. This was due to the increase in the number of ions competing for the available functions groups on the surface of biomass [26].

**Figure 3.** Effect of initial metal concentration on Chromium (VI) removal by *L. chinensis* Sonn shell. 28oC. pH 1.0, 100 rpm. 1 g biomass.
