Phosphoric Acid, Phosphates & Fertilizers Experts

Chemical reactions

Phosphoric Acid Production:

The wet phosphoric acid obtained by a gypsum process is the result of the reaction of a raw phosphate ore with sulfuric acid. The raw phosphate is usually under the form of a crystalline apatite [Ca_3(PO_4)_2]_3, CaF_2, CaCO_3.

The main reactions which can be accepted in view of a thermal balance are:

(1) Ca_3 (PO_4)_2 + 6H_2O+ 3H_2SO_43(CaSO_4, 2H_2O) + 2H_3PO_4
(2) 3CaF_2 + 3H_2SO_4 + 4H_2O + SiO_23(CaSO_4, 2H_2O) + H_2SiF_6
(3) CaCO_3 + H_2SO_4+ H_2O CaSO_4, 2H_2O+ CO_2
(4) H_3PO_4 + CaSO_4, 2H_2OCaHPO_4, 2H_2O+ H_2SO_4
(5) SiO_2 + 2H_2SiF_63SiF_4 + 2H_2O
(6) CaSO_4 + 2H_2OCaSO_4, 2H_2O
(7) Al_2O_3+ 3H_2SO_4Al_2(SO_4) + 3H_2O
(8) Fe_2O_3+ 3H_2SO_4Fe_2 (SO_4)_3 + 3H_2O
(9) MgO + H_2SO_4MgSO_4 + H_2O
(10) K_2O + H_2SO_4K_2SO_4+ H_2O
(11) Na_2O + H_2SO_4NaSO_4 + H_2O

Fluorine recovery and scrubbing:

Main reactions involved with the fluorinated compounds and water can be written:

3SiF_4 + 2H_2O2H_2SiF_6 + SiO_2 (1)

6HF + SiO_2H_2SiF_6 + 2H_2O  (2)

The first reaction is the hydrolysis of SiF_4 at the contact of the washing water to give particularly silica (on a gelatinous form). This silica is attacked (reaction 2) by the hydrofluoric acid emitted at the same time as SiF_4. So it can be seen that there will be silica precipitation only if the molar ratio HF / SiF_4 in the gaseous phase is below 2.

In the opposite case, the presence of free HF with H_2SiF_6 can be observed in the liquid phase.

In fact, SiF_6^{--} ions are not stable in an aqueous medium; the following equilibria can be observed:

SiF_6^{--} + 2H_2OSiO_2 + 4H^{+} + 6F^{-} (K_1 = 5.4 x 10^{-27})
SiF_6^{--} + 2H_2OSiF_4 + 2 F^{-} (K_2 = 0.65 x 10^{-6})

Nitric Acid Production:

Overall reaction:

NH_3 + 2O_2HNO_3 + H_2O

High temperature ammonia combustion with air and catalyst:

NH_3 + 5/4O_2NO + 3/2H_2O

Oxidation of NO with air:

NO + 1/2O_2NO_2

NO_2 absorption in water at low temperature:

NO_2 + 1/3H_2O1/3NO + 2/3HNO_3

Single Superphosphate Production

Ca_{10}(PO_4)_6F_2 + 7H_2SO_4 + 3H_2O3 Ca(H_2PO_4)_2,H_2O + 7CaSO_4 + 2HF
First step:
Ca_{10}(PO_4)_6F_2 + 10H_2SO_46H_3PO_4 + 10CaSO_4 + 2HF
Second step:
Ca_{10}(PO_4)_6F_2 + 14H_3PO_4 + 10H_2O10Ca(H_2PO_4)_2,H_2O + 2HF

Triple Superphosphate Production

Ca_5(PO_4)_3F + 7H_3PO_4 + H_2O5Ca(H_2PO_4)_2,H_2O + HF

Ammonium Phosphate production

Mono Ammonium Phosphate MAP
H_3PO_4+ NH_3NH_4H_2PO_4
Di Ammonium Phosphate DAP
H_3PO_4+ 2NH_3(NH_4)_2HPO_4

Calcium Phosphate Production

Mono Calcium Phosphate MCP
2H_3PO_4 + CaOCaH_4(PO_4)_2,H_2O
Di Calcium Phosphate DCP
2H_3PO_4 + 2CaOCa_2H_2(PO_4)_2,2H_2O

Sodium Tripolyphosphate Production

Disodium pyrophosphate or sodium acid pyrophosphate:
2NaH_2PO_4H_20 + Na_2H_2P_2O_7
Sodium polymetaphosphate:
0.5nNa_2H_2P_2O_7n(NaPO_3) +0.5NH_20
Neutral sodium pyrophosphate:
2Na_2HPO_4H_20 + Na_4P_2O_7
Sodium tripolyphosphate:
NaH_2PO_4 + 2Na_2HPO_42H_2O + Na_5P_3O_{10}