XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 177
found in HAFA or CFA (Bai et al., 2010). This low silicon
contents indicates that the acid path could be advantageous
to perform the aluminum leaching experiments. In the
bibliography, acid processes low extraction rates were often
attributed to the presence of mullite Al6Si2O13, an alumi-
nosilicate refractory to acid attack (Bai et al. 2010). The
choice of acid process also allows to access aluminum salts
of interest without additional step, by simple crystallization
after leaching and filtering of the residue. The process cho-
sen to perform the leaching experiments was therefore an
acid process using sulfuric acid, which has been studied to
leach aluminum from CFA with varying degrees of success
(Shemi et al., 2012 Wei et al., 2018).
Aluminum Leaching and Aluminum Sulfate
Crystallization
Aluminum Leaching
Leaching experiments were performed with a low ash con-
centration (0.5% ash by weight) and showed that very high
aluminum extraction rates could be reached at high tem-
perature, even in diluted sulfuric acid and with short leach-
ing times. In Figure 4 is presented the aluminum extraction
rate at 90°C as a function of acid concentration and leach-
ing duration.
Using the DoE data, the aluminum extraction rate was
modeled in the form of an equation (Equation 1), where
XAl is the aluminum extraction rate given as a percentage of
the aluminum present in the ash, and duration, tempera-
ture and sulfuric acid concentration are coded as factors,
ranging from –1 to +1 (see Table 1 for the corresponding
experimental parameters).
XAl =71.7 +1.64 *Duration
+3.09 *H2SO4 concentration
+26.35 *Temperature (1)
This model shows that the most important factor driving
aluminum extraction was temperature, while duration and
acid concentration had a much lower impact. Extraction
rates for other elements like calcium, iron, manganese and
potassium were also very high at 90°C. SEM-EDX observa-
tions of the leaching residues for high temperature experi-
ments showed that they were mainly composed of silicon,
with traces of other elements, as shown in Figure 5.
Aluminum Sulfate Crystallization
Following the leaching step, aluminum sulfate was recov-
ered by evaporating the leachates and the washing water
under vacuum at 60°C. This evaporation step was only
carried out for the leaching experiments at 90°C, as they
performed significantly better than leaching at room tem-
perature. The final product was a white powder which was
analyzed by ICP-OES. Its elemental composition is pre-
sented in Figure 6.
The product is rich in aluminum and calcium, consis-
tent with the elemental composition of the ash, with lower
amounts of potassium sodium and magnesium. No signifi-
cant difference in the composition of the final product was
observed depending on the duration of the leaching or the
sulfuric acid concentration. However further characteriza-
tion of the product is required by X-ray crystallography in
particular to determine the exact speciation of the alumi-
num and other impurities.
CONCLUSION
The physical and chemical characterization of Qualea
rosea has enabled us to identify the optimal parameters to
produce ash, which was subsequently used as a bio-ore to
perform leaching experiments. Because of its low silicon
content, the acid pathway was chosen for leaching. High
aluminum extraction rates were achieved when leaching
Qualea rosea ash at 90°C, even in diluted sulfuric acid.
Temperature was identified as the main driving parameter
of aluminum extraction. These extraction rates are higher
than those observed with typical CFAs in such condi-
tions, which could be attributed to differences in elemental
compositions of the ash. Qualea rosea ash has low silicon
Figure 2. Qualea rosea ash obtained after biomass
incineration at 900°C
found in HAFA or CFA (Bai et al., 2010). This low silicon
contents indicates that the acid path could be advantageous
to perform the aluminum leaching experiments. In the
bibliography, acid processes low extraction rates were often
attributed to the presence of mullite Al6Si2O13, an alumi-
nosilicate refractory to acid attack (Bai et al. 2010). The
choice of acid process also allows to access aluminum salts
of interest without additional step, by simple crystallization
after leaching and filtering of the residue. The process cho-
sen to perform the leaching experiments was therefore an
acid process using sulfuric acid, which has been studied to
leach aluminum from CFA with varying degrees of success
(Shemi et al., 2012 Wei et al., 2018).
Aluminum Leaching and Aluminum Sulfate
Crystallization
Aluminum Leaching
Leaching experiments were performed with a low ash con-
centration (0.5% ash by weight) and showed that very high
aluminum extraction rates could be reached at high tem-
perature, even in diluted sulfuric acid and with short leach-
ing times. In Figure 4 is presented the aluminum extraction
rate at 90°C as a function of acid concentration and leach-
ing duration.
Using the DoE data, the aluminum extraction rate was
modeled in the form of an equation (Equation 1), where
XAl is the aluminum extraction rate given as a percentage of
the aluminum present in the ash, and duration, tempera-
ture and sulfuric acid concentration are coded as factors,
ranging from –1 to +1 (see Table 1 for the corresponding
experimental parameters).
XAl =71.7 +1.64 *Duration
+3.09 *H2SO4 concentration
+26.35 *Temperature (1)
This model shows that the most important factor driving
aluminum extraction was temperature, while duration and
acid concentration had a much lower impact. Extraction
rates for other elements like calcium, iron, manganese and
potassium were also very high at 90°C. SEM-EDX observa-
tions of the leaching residues for high temperature experi-
ments showed that they were mainly composed of silicon,
with traces of other elements, as shown in Figure 5.
Aluminum Sulfate Crystallization
Following the leaching step, aluminum sulfate was recov-
ered by evaporating the leachates and the washing water
under vacuum at 60°C. This evaporation step was only
carried out for the leaching experiments at 90°C, as they
performed significantly better than leaching at room tem-
perature. The final product was a white powder which was
analyzed by ICP-OES. Its elemental composition is pre-
sented in Figure 6.
The product is rich in aluminum and calcium, consis-
tent with the elemental composition of the ash, with lower
amounts of potassium sodium and magnesium. No signifi-
cant difference in the composition of the final product was
observed depending on the duration of the leaching or the
sulfuric acid concentration. However further characteriza-
tion of the product is required by X-ray crystallography in
particular to determine the exact speciation of the alumi-
num and other impurities.
CONCLUSION
The physical and chemical characterization of Qualea
rosea has enabled us to identify the optimal parameters to
produce ash, which was subsequently used as a bio-ore to
perform leaching experiments. Because of its low silicon
content, the acid pathway was chosen for leaching. High
aluminum extraction rates were achieved when leaching
Qualea rosea ash at 90°C, even in diluted sulfuric acid.
Temperature was identified as the main driving parameter
of aluminum extraction. These extraction rates are higher
than those observed with typical CFAs in such condi-
tions, which could be attributed to differences in elemental
compositions of the ash. Qualea rosea ash has low silicon
Figure 2. Qualea rosea ash obtained after biomass
incineration at 900°C