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B.-W. Liu et al.
CaSO 4 · 2H 2 O(S) + 2NH 3 OH(aq) + CO 2 (g)
= CaCO 3 (s) + (NH 4 ) 2 SO 4 (aq) + 2H 2 O(l)
(2)
This is the gas–liquid-solid three-phase reaction system. Including the following
four reaction steps:
CO 2 + H 2 O → CO
−3
2 + 2H
+
(3)
NH 3 + H 2 O → NH
+
4 + OH
−
(4)
Ca
2+
+ CO
2−
3 → CaCO 3 ↓
(5)
2NH
+
4 + SO
2−
4 → (NH 4 ) 2 SO 4
(6)
The solubility product constant of CaCO 3 at normal temperature is Ksp = 2.8
× 10
–9 , and the solubility product constant of CaSO 4 ·2H 2 O is Ksp = 9.1 × 10
–6 .
The solubility product of CaCO 3 is much smaller than that of CaSO4·2H 2 O. The
conversion of the reaction is relatively complete. The flowchart is shown in Fig. 2.
Conversion Rate
Weigh 0.6 g of the reaction product sample which was dried to a constant mass at
105 °C ± 2 °C in advance, placed in a 250 mL beaker, and wetted with a little water.
Cover with a watch glass and add HCl solution dropwise along the mouth of the
cup until the product is completely dissolved. Then filter with filter paper, collect the
filtrate and washing liquid in a 250 mL volumetric flask, dilute to the mark with water,
shake well, this solution is the test solution. Then use a pipette to transfer 25 mL of
the test solution, place it in a 250 mL Erlenmeyer flask, add 5 mL of triethanolamine
solution, 25 mL of water and a small amount of C 21 H 14 N 2 O 7 S indicator, use NaOH
solution to make wine red, and excess 0.5 mL, use The EDTA-2Na standard titration
solution is titrated to pure blue as the end point. The actual mass M1 of CaCO 3 in the
reaction product is calculated. According to formula (1), the theoretical output M of
CaCO 3 can be calculated, and finally the mass conversion rate X of phosphogypsum
can be obtained.
X =
M1
M
× 100%
(7)
where, M1 and M represent the mass of CaCO 3 in the actual and the theoretical
output, respectively.
B.-W. Liu et al.
CaSO 4 · 2H 2 O(S) + 2NH 3 OH(aq) + CO 2 (g)
= CaCO 3 (s) + (NH 4 ) 2 SO 4 (aq) + 2H 2 O(l)
(2)
This is the gas–liquid-solid three-phase reaction system. Including the following
four reaction steps:
CO 2 + H 2 O → CO
−3
2 + 2H
+
(3)
NH 3 + H 2 O → NH
+
4 + OH
−
(4)
Ca
2+
+ CO
2−
3 → CaCO 3 ↓
(5)
2NH
+
4 + SO
2−
4 → (NH 4 ) 2 SO 4
(6)
The solubility product constant of CaCO 3 at normal temperature is Ksp = 2.8
× 10
–9 , and the solubility product constant of CaSO 4 ·2H 2 O is Ksp = 9.1 × 10
–6 .
The solubility product of CaCO 3 is much smaller than that of CaSO4·2H 2 O. The
conversion of the reaction is relatively complete. The flowchart is shown in Fig. 2.
Conversion Rate
Weigh 0.6 g of the reaction product sample which was dried to a constant mass at
105 °C ± 2 °C in advance, placed in a 250 mL beaker, and wetted with a little water.
Cover with a watch glass and add HCl solution dropwise along the mouth of the
cup until the product is completely dissolved. Then filter with filter paper, collect the
filtrate and washing liquid in a 250 mL volumetric flask, dilute to the mark with water,
shake well, this solution is the test solution. Then use a pipette to transfer 25 mL of
the test solution, place it in a 250 mL Erlenmeyer flask, add 5 mL of triethanolamine
solution, 25 mL of water and a small amount of C 21 H 14 N 2 O 7 S indicator, use NaOH
solution to make wine red, and excess 0.5 mL, use The EDTA-2Na standard titration
solution is titrated to pure blue as the end point. The actual mass M1 of CaCO 3 in the
reaction product is calculated. According to formula (1), the theoretical output M of
CaCO 3 can be calculated, and finally the mass conversion rate X of phosphogypsum
can be obtained.
X =
M1
M
× 100%
(7)
where, M1 and M represent the mass of CaCO 3 in the actual and the theoretical
output, respectively.