Optimization of Arsenic Removal Process in Waste Acid …
711
Table 4 Range analysis table
K
Control factors
A
B
C
D
K 1 j
184.25
164.5
202
198.5
K 2 j
211
86.8
101.25
176.75
K 3 j
172.25
187.5
196.5
156.75
K 4 j
137
244
204.75
172.5
R j
74
158
103.49
41.75
the min K i j was (A 4 B 2 C 2 D 3 ). Meanwhile, a larger R j means the factor has a bigger
impact on the removal of arsenic. In Table 4, the decreasing order R B > R C > R A
> R D indicates that importance of factors is as follows: the reaction time > pH >
temperature > the molar ratio of Fe/As. In addition, due to the reaction time and
pH had little difference in extremum analysis, those two elements were the main
influencing factors. The temperature and the molar ratio of Fe/As had little influence
on the removal rate of arsenic. This could also be proved from Fig. 6. Overall, the
change in temperature has little effect on G
θ in the chemical Eqs. (1, 2 and 3) of
iron.
To further explore the influence of various factors on the method, the relationship
between the levels of each factors and the removal rate of arsenic was shown in
Fig. 1. Figure 1a was effects of temperature on the rate of arsenic removal. With the
temperature rose, increased the electron exchange per unit time and speeded up the
corrosion rate of Cu–Fe battery. The removal rate of arsenic also has slight increase
in general. Final confirmation of the optimal temperature was 80 °C, but the effect
was not significant.
As can be seen from Fig. 1b, Fig. 1b was effects of the reaction time on the rate
of arsenic removal. The arsenic removal rate increased from 73.85 to 82.78% with
the reaction time increasing from 15 to 30 min, then fell after more than 30 min,
and the fluctuation range was extensive. The reaction time was the main element
affecting the arsenic removal rate. In the adsorption process, the adsorption capacity
increases rapidly with the reaction time. After more than 30 min, the adsorption
speed decreases, the resolution speed increases, and the resolution value exceeds the
adsorption value, so the optimal arsenic removal rate was reached at 30 minutes.
From Fig. 1c effects of pH on the rate of arsenic removal showed that with the rise
of pH, the removal rate of arsenic reaches a maximum value at pH value 8. Because of
different pH, iron existed in different forms in solution, Fe(II) and Fe(III) at pH 7.6 and
2.7, respectively, formed iron oxides and hydroxides precipitation. When the pH is 8,
more precipitates can be formed, thereby increasing the adsorption coprecipitation
effect are increased. For another, since the pH was neutral, iron powder corrosion
was more likely to form hydroxide adsorption. In a strong acidity or strongly alkaline
solution environment, existed the phenomenon of mutual repulsion of charges, which
negatively affects the adsorption process. In addition, Fe reduces H instead of Cu
under acidic conditions, preventing the formation of Cu–Fe battery. pH of 8 was
711
Table 4 Range analysis table
K
Control factors
A
B
C
D
K 1 j
184.25
164.5
202
198.5
K 2 j
211
86.8
101.25
176.75
K 3 j
172.25
187.5
196.5
156.75
K 4 j
137
244
204.75
172.5
R j
74
158
103.49
41.75
the min K i j was (A 4 B 2 C 2 D 3 ). Meanwhile, a larger R j means the factor has a bigger
impact on the removal of arsenic. In Table 4, the decreasing order R B > R C > R A
> R D indicates that importance of factors is as follows: the reaction time > pH >
temperature > the molar ratio of Fe/As. In addition, due to the reaction time and
pH had little difference in extremum analysis, those two elements were the main
influencing factors. The temperature and the molar ratio of Fe/As had little influence
on the removal rate of arsenic. This could also be proved from Fig. 6. Overall, the
change in temperature has little effect on G
θ in the chemical Eqs. (1, 2 and 3) of
iron.
To further explore the influence of various factors on the method, the relationship
between the levels of each factors and the removal rate of arsenic was shown in
Fig. 1. Figure 1a was effects of temperature on the rate of arsenic removal. With the
temperature rose, increased the electron exchange per unit time and speeded up the
corrosion rate of Cu–Fe battery. The removal rate of arsenic also has slight increase
in general. Final confirmation of the optimal temperature was 80 °C, but the effect
was not significant.
As can be seen from Fig. 1b, Fig. 1b was effects of the reaction time on the rate
of arsenic removal. The arsenic removal rate increased from 73.85 to 82.78% with
the reaction time increasing from 15 to 30 min, then fell after more than 30 min,
and the fluctuation range was extensive. The reaction time was the main element
affecting the arsenic removal rate. In the adsorption process, the adsorption capacity
increases rapidly with the reaction time. After more than 30 min, the adsorption
speed decreases, the resolution speed increases, and the resolution value exceeds the
adsorption value, so the optimal arsenic removal rate was reached at 30 minutes.
From Fig. 1c effects of pH on the rate of arsenic removal showed that with the rise
of pH, the removal rate of arsenic reaches a maximum value at pH value 8. Because of
different pH, iron existed in different forms in solution, Fe(II) and Fe(III) at pH 7.6 and
2.7, respectively, formed iron oxides and hydroxides precipitation. When the pH is 8,
more precipitates can be formed, thereby increasing the adsorption coprecipitation
effect are increased. For another, since the pH was neutral, iron powder corrosion
was more likely to form hydroxide adsorption. In a strong acidity or strongly alkaline
solution environment, existed the phenomenon of mutual repulsion of charges, which
negatively affects the adsorption process. In addition, Fe reduces H instead of Cu
under acidic conditions, preventing the formation of Cu–Fe battery. pH of 8 was