**4.1. Arsenic removal using modified clay minerals**

Mishra and Mahato [40] evaluated the effectiveness of Fe and Mn pillared bentonite clay in As(V) and As(III) removal from groundwater. Maximum As(III) and As(V) adsorption capacities of 17.57 and 25.77 μg/g were observed for Fe pillared bentonite while adsorption capacities of 25.77 and 26.17 μg/g were observed for Mn pillared bentonite clay. This was higher by many folds compared to 4.31 and 4.33 μg/g for raw bentonite clay. This was attributed to increased surface area in the pillared bentonite and also increased charge density in the pillared clay.

was better than the capacity achieved with unmodified bentonite. Gitari et al. [20] reported maximum adsorption capacity of 2.91 mg/g for the Fe3+ modified bentonite clay which was also better than the unmodified bentonite. The main factor which was leading to improved sorption fluoride capacity was the increased surface area that corresponds to availability of more active sites for fluoride ion adsorption. Furthermore, modification of clay mineral my high density charges polycations increases the amount of positive charges in the surface of

**Table 2.** Comparison of the adsorption capacity between raw and modified clay toward arsenic and fluoride.

**Table 2** summarizes the comparison between raw and modified clay soils toward fluoride and arsenic adsorption from water. It is observed that the adsorption of fluoride and arsenic

General mechanism involved for arsenic and fluoride removal using clay mineral can be summarized by the following three main steps: (i) Mass transfer of ions to the external of the adsorbent, (ii) adsorption of ions on the external particle surface and (iii) Intra-particle diffusion of ions from the exterior surface and the exterior surface and possible exchange with elements on the pore surface inside particles [30, 43]. These major three steps were observed during the

coated bentonite by Mudzielwana et al., [44]. Besides these

**5. Mechanisms for arsenic and fluoride removal using clay soils**

adsorbent leading to increased sorption capacity of anions.

increases by many fold after clay modification.

adsorption of fluoride onto MnO<sup>2</sup>

**Adsorbent CEC** 

CTAMB-Fe montmorillonite

NB: (−) = not reported.

**(meq/100 g)**

**Surface area (m2 /g)**

Kaolinite — 33 As(V) 5 40 0.86 [32] Montmorillonite — 58 As(V) 5 40 0.68 [32] Illite — 28 As(V) 5 40 0.54 [32] Moroccan clays 35 22.5 As(V) 7 25 1.07 [33] Smectite rich clay 79.9 20.35 F<sup>−</sup> 2 8 0.21 [23] Montmorillonite — 18.5 F<sup>−</sup> 6.0 8 0.26 [35] Mixed Mukondeni clay 137.7 35.46 F<sup>−</sup> 2 150 0.08 [24]

Fe-montmorillonite — — As(V) 4–10 4 15.15 [25] Mg2+ bentonite — — F<sup>−</sup> 3–10 3 2.26 [41] Fe3+ bentonite 188.9 49.95 F<sup>−</sup> 2–10 20 2.29 [20] Al3+ bentonite 183.3 33.1 F<sup>−</sup> 2–12 10 5.7 [22]

**Adsorbate pH Adsorbent** 

Mineralogical and Chemical Characteristics of Raw and Modified Clays and Their Application…

— — As(V) 4–10 4 8.85 [25]

**dosage (g/L)**

**Adsorption capacity (mg/g)**

http://dx.doi.org/10.5772/intechopen.74474

**Ref**

53

Ren et al. [25] intercalated Fe polycations and cetyltrimethylammonium bromide (CTMAB) onto montmorillonite clay mineral and test it for arsenic removal. The results showed that CTMAB had diffused into the interlayers of the montmorillonite minerals while Fe polycations were adsorbed on the outer surface and had formed flocculent particles. When tested for arsenic removal, CTMAB-Fe montmorillonite and Fe montmorillonite showed a maximum adsorption capacities of 8.85 and 15.15 mg/g for As(V), respectively, and 13.89 and 16.13 mg/g for As(III). Furthermore, the optimum adsorption capacities were observed at wide range of pH of 4–10.

### **4.2. Fluoride removal using modified clay minerals**

Several studies have been reported concerning the adsorption of fluoride using chemically modified clay minerals and the results showed improved adsorption efficiency as compared to unmodified clay soils. Kamble et al. [41] reported better sorption capacity for La, Mn and Mg oxides incorporated bentonite clay compared to bare bentonite. Efficiency of magnesium incorporated bentonite in adsorption of fluoride has also been evaluated by Thakre et al. [42] and maximum adsorption capacity of 2.26 mg/g was achieved over a wide range of pH which Mineralogical and Chemical Characteristics of Raw and Modified Clays and Their Application… http://dx.doi.org/10.5772/intechopen.74474 53


**Table 2.** Comparison of the adsorption capacity between raw and modified clay toward arsenic and fluoride.

Lenoble et al. [21] pillared montmorillonite clay using titanium, iron and aluminum as pillaring solution. Their results confirmed that pillaring increases the basal spacing and the specific surface area by many folds. These results were confirmed by Mishra and Mahato [40] who also observed increased in both specific surface area for Mn and Fe pillared bentonite clay. Beside the side the change in basal spacing and chemical oxide content in the pillared clays, the whole process of pillaring does not change the mineralogical composition of the clay.

Mishra and Mahato [40] evaluated the effectiveness of Fe and Mn pillared bentonite clay in As(V) and As(III) removal from groundwater. Maximum As(III) and As(V) adsorption capacities of 17.57 and 25.77 μg/g were observed for Fe pillared bentonite while adsorption capacities of 25.77 and 26.17 μg/g were observed for Mn pillared bentonite clay. This was higher by many folds compared to 4.31 and 4.33 μg/g for raw bentonite clay. This was attributed to increased surface area in the pillared bentonite and also increased charge density in the pillared clay.

Ren et al. [25] intercalated Fe polycations and cetyltrimethylammonium bromide (CTMAB) onto montmorillonite clay mineral and test it for arsenic removal. The results showed that CTMAB had diffused into the interlayers of the montmorillonite minerals while Fe polycations were adsorbed on the outer surface and had formed flocculent particles. When tested for arsenic removal, CTMAB-Fe montmorillonite and Fe montmorillonite showed a maximum adsorption capacities of 8.85 and 15.15 mg/g for As(V), respectively, and 13.89 and 16.13 mg/g for As(III). Furthermore, the optimum adsorption capacities were observed at wide range of pH of 4–10.

Several studies have been reported concerning the adsorption of fluoride using chemically modified clay minerals and the results showed improved adsorption efficiency as compared to unmodified clay soils. Kamble et al. [41] reported better sorption capacity for La, Mn and Mg oxides incorporated bentonite clay compared to bare bentonite. Efficiency of magnesium incorporated bentonite in adsorption of fluoride has also been evaluated by Thakre et al. [42] and maximum adsorption capacity of 2.26 mg/g was achieved over a wide range of pH which

**4.1. Arsenic removal using modified clay minerals**

52 Current Topics in the Utilization of Clay in Industrial and Medical Applications

**Figure 4.** Schematic diagram of a pillared clay [40].

**4.2. Fluoride removal using modified clay minerals**

was better than the capacity achieved with unmodified bentonite. Gitari et al. [20] reported maximum adsorption capacity of 2.91 mg/g for the Fe3+ modified bentonite clay which was also better than the unmodified bentonite. The main factor which was leading to improved sorption fluoride capacity was the increased surface area that corresponds to availability of more active sites for fluoride ion adsorption. Furthermore, modification of clay mineral my high density charges polycations increases the amount of positive charges in the surface of adsorbent leading to increased sorption capacity of anions.

**Table 2** summarizes the comparison between raw and modified clay soils toward fluoride and arsenic adsorption from water. It is observed that the adsorption of fluoride and arsenic increases by many fold after clay modification.
