68
The materials studied show an outstanding efficiency to remove fluoride from
water. However, it is essential to consider that the contaminate concentration, solution pH and temperature, surface area of adsorbent, and the contact time are parameters that affect the fluoride adsorption capacity (Yadav et al. 2018). The pH is an
essential factor affecting defluorination (Ma et al. 2009), for instance, the adsorbent
surface at alkaline pH has a negative charge while at acid pH is highly protonated.
Therefore, the high fluoride adsorption capacity at acid pH can be attributed to an
increase in attractive forces between the adsorbate and adsorbent (Rajan and
Alagumuthu 2013; Vences- Alvarez et al. 2015).
As for the adsorption capacity, this can vary depending on the adsorbent material. In general terms, the arsenic adsorption capacity is between 2 and 200 mg/g
using metal and bimetallic oxyhydroxides (Zhang et al. 2003; Dou et al. 2011b;
Basu and Ghosh 2013; Chaudhry et al. 2017; Dou et al. 2018). Chen et al. 2014
synthesized iron–cerium alkoxide with a high surface area and abundant surface
functional groups. The bimetallic oxide produced by using a molar ratio of 5:1
for Fe:Ce, respectively, exhibited the highest adsorption capacities for both As(V)
and As(III) (206 and 266 mg/g, respectively). As for the fluoride adsorption capacity, it is between 2 and 250 mg/g (Bhatnagar et al. 2011; Loganathan et al. 2013;
Velazquez-Jimenez et al. 2015). Lv et al. (2007) employed MgAl–CO 3 layered double hydroxides to treat high fluoride concentration solutions. The MgAl–CO 3 maximum adsorption capacity was 319.8 ± 5.7 mg/g at an initial fluoride concentration
between 1000 and 1500 mg/L, and in a pH range of 5–7.
An example of the application of alumina in the simultaneous arsenic and fluoride removal from water is the system called ArCIS- UNR. This is a hybrid process
that integrates adsorption, coagulation and filtration: using poly-aluminum chloride
as a coagulant, followed by two filtration units (upflow coarse gravel filtration and
rapid sand filtration). This process has been successfully implemented in large- scale
plants in Argentina, and has treated groundwater with arsenic concentrations of
100–150 μg/L and fluoride concentrations of 1.7–2.5 mg/L. The results of this
research indicate that the optimum pH range for the removal of arsenic and fluoride
was 6.3–7.3 and 5.2–6.2, respectively. The efficiencies reached ranged between 75
and 85% for arsenic and between 50 and 55% for fluoride. However, the disadvantage of this process is that at pHs below 7.0, the residual aluminum begins to
increase (Ingallinella et al. 2011).
Other material that has been succesfully employed for the removal of asernic
from water is iron based ion exchange resin. German and coworkers (German et al.
2019) reported the performance of a community scale hybrid anion exhange system
as a long-term solution for arsenic contaminated growndwater. The hybrid ionexchange materials are composed of cerium or zirconium oxide nanoparticles dispersed in an anionic exchange polymer resin (Cumbal et al. 2003; German et al.
2014). Three of the arsenic mitigation systems were monitored during 24 months of
long-term self-sustainable operation to assess the efficiency and profitability of the
systems. The systems were designed to provide high-quality water to 200 families,
that is, between 500 and 1000 people. Hybrid ion-exchange materials can be regenerated efficiently compared to activated alumina (German et al. 2019).
E. Vences-Alvarez et al.
The materials studied show an outstanding efficiency to remove fluoride from
water. However, it is essential to consider that the contaminate concentration, solution pH and temperature, surface area of adsorbent, and the contact time are parameters that affect the fluoride adsorption capacity (Yadav et al. 2018). The pH is an
essential factor affecting defluorination (Ma et al. 2009), for instance, the adsorbent
surface at alkaline pH has a negative charge while at acid pH is highly protonated.
Therefore, the high fluoride adsorption capacity at acid pH can be attributed to an
increase in attractive forces between the adsorbate and adsorbent (Rajan and
Alagumuthu 2013; Vences- Alvarez et al. 2015).
As for the adsorption capacity, this can vary depending on the adsorbent material. In general terms, the arsenic adsorption capacity is between 2 and 200 mg/g
using metal and bimetallic oxyhydroxides (Zhang et al. 2003; Dou et al. 2011b;
Basu and Ghosh 2013; Chaudhry et al. 2017; Dou et al. 2018). Chen et al. 2014
synthesized iron–cerium alkoxide with a high surface area and abundant surface
functional groups. The bimetallic oxide produced by using a molar ratio of 5:1
for Fe:Ce, respectively, exhibited the highest adsorption capacities for both As(V)
and As(III) (206 and 266 mg/g, respectively). As for the fluoride adsorption capacity, it is between 2 and 250 mg/g (Bhatnagar et al. 2011; Loganathan et al. 2013;
Velazquez-Jimenez et al. 2015). Lv et al. (2007) employed MgAl–CO 3 layered double hydroxides to treat high fluoride concentration solutions. The MgAl–CO 3 maximum adsorption capacity was 319.8 ± 5.7 mg/g at an initial fluoride concentration
between 1000 and 1500 mg/L, and in a pH range of 5–7.
An example of the application of alumina in the simultaneous arsenic and fluoride removal from water is the system called ArCIS- UNR. This is a hybrid process
that integrates adsorption, coagulation and filtration: using poly-aluminum chloride
as a coagulant, followed by two filtration units (upflow coarse gravel filtration and
rapid sand filtration). This process has been successfully implemented in large- scale
plants in Argentina, and has treated groundwater with arsenic concentrations of
100–150 μg/L and fluoride concentrations of 1.7–2.5 mg/L. The results of this
research indicate that the optimum pH range for the removal of arsenic and fluoride
was 6.3–7.3 and 5.2–6.2, respectively. The efficiencies reached ranged between 75
and 85% for arsenic and between 50 and 55% for fluoride. However, the disadvantage of this process is that at pHs below 7.0, the residual aluminum begins to
increase (Ingallinella et al. 2011).
Other material that has been succesfully employed for the removal of asernic
from water is iron based ion exchange resin. German and coworkers (German et al.
2019) reported the performance of a community scale hybrid anion exhange system
as a long-term solution for arsenic contaminated growndwater. The hybrid ionexchange materials are composed of cerium or zirconium oxide nanoparticles dispersed in an anionic exchange polymer resin (Cumbal et al. 2003; German et al.
2014). Three of the arsenic mitigation systems were monitored during 24 months of
long-term self-sustainable operation to assess the efficiency and profitability of the
systems. The systems were designed to provide high-quality water to 200 families,
that is, between 500 and 1000 people. Hybrid ion-exchange materials can be regenerated efficiently compared to activated alumina (German et al. 2019).
E. Vences-Alvarez et al.