JPS59199095A - Treatment of waste water generated in producing phosphoric acid by performing wet decomposition of phosphate ore with sulfuric acid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater generated during the production of phosphoric acid by wet decomposition of phosphate rock with sulfuric acid. It is piled up.

Phosphoric acid can be produced from phosphate rock by thermal and wet decomposition methods. Thermal methods, which account for about 10% of the world's production of phosphoric acid, involve decomposing phosphate rock with silicic acid and coke in electric resistance furnaces at high temperatures, and burning the resulting elemental phosphorus to produce phosphorus oxide, In particular, P401o is obtained, which is subsequently hydrolyzed to give phosphoric acid. In contrast, in the wet process, which accounts for about 90% of the marginal yield of phosphoric acid, phosphate rock is decomposed with mineral acids, especially sulfuric acid. In this case, during the wet decomposition with sulfuric acid, the calcium contained in the phosphate rock precipitates as so-called phosphate slag (Ca5O,.xH20). This phosphoric acid sludge, which is usually produced in the form of sludge at the end of the phosphoric acid production process, cannot be immediately put to other uses due to the impurities it contains. For this purpose, a moon I is required to further sheath the sesokousurano// which is produced in the first place, but this is often abandoned for economic reasons. 1. Continuing to use the raw material for wet phosphoric acid production
Unless otherwise specified, this can be removed today in particular in the following way.

1 After diluting Setsukousuranoji as appropriate,
Delivered by underwater vessel.

2. After properly drying the Sesokowo and Setsukosuranoji, pile them up in a dry state.

3. Deposit Cenokoura Soji in liquid form.

Of these three methods, the last one is used most often in practice. However, a significant drawback of this method is that the process wastewater adhering to the slag is highly acidic and contains impurities, especially large amounts of fluoride and ligates. Therefore, it is not possible to immediately dump this wastewater into a drainage ditch. Furthermore, there is a risk that groundwater contamination may be caused by uncontrolled wastewater discharge from the leakage points of the Senokousurasoji dump.

It is therefore an object of the invention to take into account, in a process of the type mentioned at the outset, a suitable treatment of the waste water flowing out from the Sesoko sludge deposits, which according to the invention can be recycled in a suitable and powerful manner. use, thereby avoiding disposal of the wastewater into drains and other environmental pollution.

A method which serves to solve this problem is characterized by the application of method features a) to C) of claim 1 according to the invention.

Details of the method according to the A17 invention are clear from claims 2 to 4, and will now be explained with reference to the flow sheet shown in the drawings. In this case, the flow sheet shows only those process steps which are absolutely necessary for this purpose. The details of the phosphoric acid production equipment described above are not shown in the flowsheet. However, the phosphoric acid production and all the steps shown in the flowsheet can be carried out using conventional machinery and equipment for this purpose. The flow sheet at the same time serves to illustrate an example. In this case, the water (flowing from the Senokousuranoji deposit) contains mainly F, SO, P2O5 and S as impurities. i has O2.

This wastewater has an I) value of 12 to 2.0 and is introduced via line 2 into the first neutralization stage, where it is first brought to a pH value of 25 to 4.5 by addition of calcium ions. In this case, approximately 99% of the fluorine-containing components present in the wastewater
% is precipitated as fluoride. This calcium fluoride-rich sludge is removed from the first neutralization step 3 by a cow, and the wastewater from which the sludge has been removed is introduced into the second neutralization step 6 through a conduit 5. Here, 156 water is further added with calcium ions.
H (Wi), which in particular reduces the P2O5 content still present in the wastewater by about 95%, as well as S
The io2 content is reduced by about 90%.

This raw sludge is separated from the wastewater again and a second
It is taken out from the neutralization step 6. The after-treated and desludged wastewater d leaving the second neutralization stage 6 has only the following impurities:

F < 10 ppm P205 × 30 ppm 5io2 < 150 pprn In this case, on the surprised skewer, two separated from each other according to the invention
It has been found that by neutralizing in two steps, a significantly better wastewater purification effect can be obtained than by carrying out step 1j in just one step.

The purified wastewater is treated with phosphoric acid (IQ process 9
The water is returned to the water tank, where it is reused as cleaning water. Of course, by this measure the demand for fresh water in the phosphoric acid filtration step is correspondingly reduced.

The sludge removed from the first and second neutralization stages 4 and 7 can be fed together to a common mechanical dewatering stage 10, where it is dewatered to a residual water content as low as 70% by weight. .

Following this, the sludge enters a drying step 11, which may be configured as a spray dryer or a drum dryer, for example, in which complete drying of the sludge takes place. This deworming dry material can be removed at 12 and added as a charge in the production of, for example, hydrofluoric acid. The hot dryer waste is removed via conduit 13 and available for heating the after-treated wastewater in conduit δ in a heat exchanger system. That is, if the post-treated wastewater used as cleaning medium has a temperature of >30'C;
It was found that the cleaning effect in the phosphoric acid filtration step 9 can be significantly improved. ) In C1-7-1-, the first
and the sludge from the second neutralization step are subsequently processed together. However, it is of course also possible to treat these sludges separately from each other. Koti
This is carried out in particular if special utilization is possible for the carunium fluoride from the first neutralization step.

Following normal vortexing and a second neutralization step - °6, the resulting post-treated wastewater is completely returned via line 8 to the phosphoric acid filtration step 9, where it is reused as wash water. I can do it. However, if this is not possible in particular cases, it is possible to take off the excess after-treated waste water via the conduit 15 and process it further in the evaporative concentration stage 16. This is the case, for example, in the case of production failures in the preceding phosphoric acid production plants, or in the case of increased waste water volumes from the Setsukousurasozhi dam due to sludge or increased sediment volumes. Finally, a partial evaporative concentration of the after-treated wastewater may also be provided when an unacceptable enrichment of certain contents dissolved in the closed wastewater circuit occurs.

During the evaporative concentration step 16, the j
56 parts of water are divided into distillate and brine. The distillate, which is actually distilled water, is removed via conduit 17 and can be used within the plant as fresh water, cooling water or boiler water. The brine in concentrated form with impurities resulting from the evaporative concentration step 16 is removed via a conduit 18, and the sludge from the neutralization step is transferred to the mechanical dewatering step 1.
Added before 0. Therefore, this method avoids having to dump the wastewater flowing out of the Setsukousurano/Sump into a drain. In this case, by returning the post-treated water to the phosphoric acid filtration step 9, the demand for fresh water during phosphoric acid production is reduced accordingly.

[Brief explanation of the drawing]

The drawing is a flow sheet illustrating one embodiment of the method according to the invention. DESCRIPTION OF SYMBOLS 1... Senokousuranon deposition site, δ... 1st L1 concentration process, 6... 2nd neutralization process, 9... Phosphoric acid filtration process 10... Dehydration process, 11... Drying process, 1 Cow···
Heat exchanger, 16...evaporation concentration step

Claims (1)

[Scope of Claims] 1. A method for depositing sesoko sludge produced during the decomposition of phosphate rock in liquid form in a dump site, in order to treat wastewater produced during the production of phosphoric acid by wet decomposition of phosphate rock with sulfuric acid. , a) The wastewater flowing out from the sesoko sludge deposits is treated in the first neutralization step by the addition of calcium ions.
．． Bringing to a pH value of 5-45 and separating its original sludge, the sludge-removed wastewater is then treated in a second neutralization step, also by the addition of calcium ions, to a pH value of 9-13.
1) After subsequent sludge separation, the water is returned to the phosphoric acid filtration step in whole or in part as wash water. b) the sludges resulting from both neutralization steps are further treated individually or together in a drying step after corresponding mechanical dewatering, and C) the excess waste water after treatment is further treated in an evaporative concentration step, with the A phosphoric acid filtration process characterized in that the distillate produced therein which is not returned to the phosphoric acid filtration step is used as /11 water, cooling water or mostly as irrigating water, and the resulting salt solution is dried together with the sludge from both neutralization steps. A method for treating wastewater generated when producing phosphoric acid by wet decomposition of ore with sulfuric acid. 2. The process according to claim 1, wherein the sludge produced during the neutralization step of the wastewater is dewatered to a residual water content of less than 70% by weight by mechanical dewatering before being introduced into the drying step. 3. The waste gas from the drying process is used directly or indirectly to heat the post-treated wastewater, and the wastewater is returned to the phosphoric acid filtration process as wash water, or The method described in Section 2. 4. The method according to any one of claims 1 to δ, wherein the post-treated wastewater having a temperature of 30° C. is fed to a phosphoric acid filtration step.