Bone chars were obtained using the synthesis conditions
reported by Rojas-Mayorga et al. [7]. This synthesis was performed
via the pyrolysis of bovine bone wastes at 700 ◦C for 2 h under an
inert atmosphere of N2. A tubular furnace Carbolite Eurotherm CTF
12165/550 with a quartz sample holder was used for the bone
char preparation. The bone chars were washed with deionized
water until obtaining a constant pH in the washing solution and,
finally, they were dried overnight before their use in metal surface
modifications and fluoride adsorption experiments. This adsorbent
showed a specific surface area of 110 m2/g, total pore volume of
0.233 cm3/g, and a pore size of 8.47 nm [7].
The surface chemistry of bone chars was modified using iron
and aluminum salts. Fig. S1 of supplementary material illustrates
the experimental procedure used for the metallic doping of this
adsorbent. Basically, this stage was performed using 1 g of bone
char, which was mixed with a metallic solution during a specific
contact time at a constant reaction temperature. An experimental
design based on Taguchi’s L9 orthogonal array was used in this
stage. This experimental design allowed to study the effect of the
metallic doping conditions on the adsorption properties of bone
char and to identify the best conditions for enhancing its fluoride
uptakes. Four variables were identified via preliminary studies
and they were included in the L9 orthogonal array, see Table 1.
These variables are: (a) the concentration of the metallic specie
(iron or aluminum) used in the surface modification: 0.1, 0.5 and
1.0 M, (b) the reaction time for the metal impregnation of bone
char: 2, 4 and 6 h, (c) the ratio of bone char/metal solution used
in the metal impregnation: 1/10, 1/20 and 1/30 g/mL and (d) the