EP0684859B1 - P4s10 waste disposal method - Google Patents

Description

The present invention relates to a process for eliminating waste formed during the manufacture, packaging and use of phosphorus polysulphides and in particular of P ₄ S ₁₀ .

P ₄ S ₁₀ is prepared from liquid sulfur and liquid phosphorus in substantially stoichiometric quantities at temperatures between 300 ° C and 515 ° C.

The products obtained generally pass through a packed column allowing to retain the impurities likely to come from the reagents as well as by-products likely to form during the reaction.

Then the products are condensed in a tubular exchanger and exit in liquid form which can undergo rapid cooling to lead to a solid which can be crushed and finally conditioned in metal containers or drums.
The waste formed during the preparation and packaging of P ₄ S ₁₀ comes essentially from the cleaning of devices such as scaly, conveyor screw, condensers, etc. and happen to be in the form of powders or flakes which represent at least 10% of all waste; periodic emptying of the reactor and happen to be in the form of large blocks which represent approximately 25% of the total waste; washing the return containers and are in the initial form of flakes or powders which represent the largest amount of waste estimated at around 55% and of the vents and effluents which happen to be initially in the form of gas containing P dust ₄ S ₁₀ , traces of H ₂ S. This latter source represents some 10% of all waste.

Initially, the majority of the waste happens to be in solid form. This is particularly the case for waste from emptying the reactor, cleaning of appliances and containers. This waste cannot be recycled in the manufacturing cycle for reasons including quality.

They consist mainly of P ₄ S ₁₀ associated with small quantities of phosphorus polysulphides such as P ₄ S ₉ , P ₄ S ₇ . It also detects organic impurities and metallic impurities such as iron, arsenic, nickel, chromium, antimony.

This waste is more or less sensitive to hydrolysis and cannot be stored in landfills or buried because the slow hydrolysis of this waste is likely to produce significant quantities of gas (H ₂ S) and toxic materials likely to irreparably contaminate groundwater.

Also, for better environmental protection of standards rigorous regarding the disposal of phosphorus and sulfur wastes have been established to avoid or even prohibit any improper storage of untreated waste in discharges or their elimination, in lakes, rivers or seas.

Patent DD 122 058 teaches that the waste originating from the synthesis of P ₄ S ₁₀ can be treated with a sodium hydroxide solution and then injection of chlorine.

This treatment makes it possible to transform the waste essentially consisting of P ₄ S ₁₀ into a mixture of products consisting of phosphates, phosphites, thiophosphates, sulfates and chlorides.

However, this method has a number of drawbacks.

In particular, it requires the use of large quantities of reagents. Indeed, for a ton of P ₄ S ₁₀ to be treated, it is necessary to use not less than 35 m ³ of 20% sodium hydroxide solution (approximately 42 tonnes) and 6.3 tonnes of chlorine.

In patent DD 156 902, the operation is similar except that it is used less reagents including less soda.

The waste is treated with sodium hydroxide solution and then undergoes a chlorine treatment in order to obtain a pH close to 7-8. Chlorination is continued while adding sodium hydroxide to maintain said pH at 7-8.

Thus for a tonne of P ₄ S ₁₀ to be treated, 1.3 to 1.6 tonnes of chlorine and 10 m ³ of 20% sodium hydroxide are used.

However, this method has the disadvantage of generating quantities significant elemental sulfur and also has the disadvantage of using chlorine.

US Patent 4,301,014 relates to the treatment of water resulting from the elimination of waste from the manufacture of P ₄ S ₁₀ . This waste is hydrolyzed with water, then brought into contact with lime in order to precipitate the sulphides, sulphites, sulphates and phosphates in the form of calcium salts, then to treat the solution freed from these salts by an oxidant such as calcium chlorine or hypochlorite at a pH close to 9 in order to reduce the "chemical oxygen demand" (DOC) before discharge.

This process has many drawbacks. First, hydrolysis requires significant quantities of water, approximately 235 m ³ per tonne of P ₄ S ₁₀ to be treated, which requires very large reactors, which is prohibitive for an economical industrial process. Furthermore, this hydrolysis generates significant amounts of H ₂ S requiring specific equipment for its destruction.

Then, this process requires many filtration operations: filtration after hydrolysis, filtration after precipitation with lime, filtration after chlorination, which are likely to increase the cost and complexity of the operation of the process.

• mettre en solution lesdits déchets par attaque alcaline, à
• collecter les différentes solutions obtenues dans un bac tampon, et à
• oxyder biologiquement les solutions ainsi obtenues maintenues à un pH supérieur à 7, contenant des thiophosphates de formule Me₃ PS_x O_4-x dans laquelle Me représente NH₄, un métal alcalin tel que Na, K et x est un nombre entier allant de 1 à 4, des phosphates, des sulfures et des phosphites avant rejet sous forme de solution constituée essentiellement par des sulfates et des phosphates.

A simple and economical process has now been found for eliminating waste formed during the manufacture, packaging and use of phosphorus polysulphides, said process being characterized in that it consists in:

• dissolving said waste by alkaline attack,
• collect the different solutions obtained in a buffer tank, and
• biologically oxidize the solutions thus obtained maintained at a pH greater than 7, containing thiophosphates of formula Me ₃ PS _x O _4-x in which Me represents NH ₄ , an alkali metal such as Na, K and x is an integer ranging from 1 to 4, phosphates, sulfides and phosphites before rejection in the form of a solution consisting essentially of sulfates and phosphates.

This process is particularly applicable to waste from the manufacture, packaging and use of P ₄ S ₁₀ .

According to the present invention, the waste can be dissolved alkaline in different ways depending on the one hand, their origin and, on the other hand their physical state.

The vents and / or gaseous effluents originating in particular from the reactor and from the conditioning consisting essentially of suspended powders and traces of H ₂ S are generally killed by an alkaline solution which consists of backwashing with an alkaline solution (A) .

Waste from washing containers with pressurized water are introduced into an alkaline solution (B).

"Solid" waste in different forms (plus blocks or less coarse, powders, scales) from both washing devices such as scaly, conveyor screw, reactor, condensers and products outside specifications are collected and then introduced into an alkaline solution (C).

The different alkaline solutions (A), (B) and (C) are generally soda, potash or ammonia solutions. These solutions may have the same or different concentrations of alkaline agent. Of preferably, sodium hydroxide solutions with a weight concentration will be used in NaOH of between 5% and 30% and preferably between 10% and 20%.

The molar ratio Rm = P 4 S 10 NaOH is at least 13
and preferably between 15 and 32.

Whether the waste is treated separately or simultaneously, we operate preferably by introducing the waste into the alkaline solution with stirring at a temperature between 20 ° C and 80 ° C and preferably between 25 ° C and 60 ° C.

The duration of the dissolution can vary to a large extent. She is generally based on the physical state of the waste.

It is at least equal to 30 minutes and, preferably, between 2 and 6 hours.

The different solutions (A), (B) and (C) are collected, in particular in a tray called "buffer".

The solution obtained is generally clear.

In the case where the solution was carried out with sodium hydroxide solutions, the buffer tank solution consists of sodium thiophosphates of formula Na ₃ PS _x O _4-x ; x being an integer ranging from 1 to 4, Na ₂ S, sodium phosphates and sodium phosphite.

The final solution obtained must be at a pH greater than 7 in order to avoid any release of H ₂ S.

This is advantageously achieved by using at the time of setting alkaline solution a slight excess of soda which is at most equal to 5%.

This alkaline solution operation is generally carried out in reactors with stirring system, temperature measurement, heating and cooling systems.

In the event of a slight insoluble matter, it is possible to separate by known methods such as filtration or centrifugation.

The alkaline solution thus obtained is then biologically oxidized.

To this end, the solution is introduced into a so-called "activated sludge" reactor. a biological station treating wastewater coming in particular from a site industrial.

These activated sludges are made up of microorganisms and bacteria which, in an aerobic environment, destroy the carbon pollution of industrial effluent (decrease in COD) and also oxidize sulfides and thiophosphates.

The "activated sludge" reactor is supplied with air or pure oxygen thus allowing the ventilation of the medium.

The pH of the medium must be as stable as possible and as close as possible of neutrality, see slightly basic.

Therefore, although the effluent to be treated is generally only a low part of the diet of the biological station, avoid a content of soda free from this effluent too high.

After passing through the reactor, the effluent is separated from the sludge which is made up of micro-organisms and bacteria, in a clarifier before rejection.

The decanted sludge is largely recycled in the reactor, a part of the settled sludge is conveyed to a thickener where the maximum water. The water is recycled to the reactor while the sludge is disposed of in a landfill.

The advantage of the process according to the present invention is that it eliminates waste in the form of aqueous effluents consisting essentially of sulfates and phosphates in accordance with the standards in force concerning discharges.

The following example illustrates the invention.

We carried out an industrial test which led to the treatment of an amount equal to 6.4 tonnes consisting of solid waste formed during the preparation of P ₄ S ₁₀ from the cleaning of devices such as reactor, scaly, conveyor screw and products out of specification.

To do this, 8 effluents of approximately 15 m ³ are prepared.

Effluent preparation

650 kg to 850 kg of the abovementioned waste are gradually and manually introduced into a 15 m ³ stirred tank containing approximately 5.4 m ³ of sodium hydroxide at 20% by weight.

The introduction of the waste is regulated in such a way that the temperature does not exceed 50 ° C.

The duration of the operation is approximately 6 hours.

Once the introduction is complete, water is introduced to complete the level up to 15 m ³ .

It is ensured throughout the duration of the operation that the quantity of sodium hydroxide used is greater than the stoichiometric quantity of sodium hydroxide necessary for the hydrolysis so as to obtain an effluent containing free sodium hydroxide making it possible to avoid any release of H ₂ S.

• la concentration en phosphates totaux
• la concentration en soude libre.

On each effluent we determine:

• the concentration of total phosphates
• the concentration of free soda.

The table below collates the results obtained. EFFLUENT N ° CONCENTRATION IN TOTAL PHOSPHATES (g / l) CONCENTRATION IN FREE SODA (g / l) 1 42.9 50.8 2 36 13.4 3 32 22.7 4 52 16.9 5 50 16.9 6 37.5 25.8 7 48.8 25.6 8 47.5 11.6

• Na₃PS_xO_4-x avec x allant de 1 à 4,
• Phosphates de sodium
• Na₂S
• Na₃PO₃

The NMR analysis of P ³¹ indicates that the effluents consist essentially of:

• Na ₃ PS _x O _4-x with x ranging from 1 to 4,
• Sodium phosphates
• Na ₂ S
• Na ₃ PO ₃

Biological oxidation of effluents (Plate 1/2)

Each aqueous effluent (1) previously prepared is sent to a biological treatment station. It is deposited in a tank (2) continuously supplied with effluents of the same nature (3) (sodium hydroxide solutions consisting of Na ₂ S). The content of this tank is then injected continuously (4) into the "active" sludge reactor (5) at the same time as all of the wastewater from an industrial site (6).

"Activated" sludge consists of microorganisms and bacteria evolving in aerobic environment.

The ventilation of the medium is ensured by an air supply (7) and also by a supply of pure oxygen (8).

Oxidation takes place at atmospheric pressure, at room temperature and at a pH of around 8.

After passing through the reactor (5) the effluent (9) is separated from the sludge in a clarifier (10) before rejection (11).

Decanted sludge is largely recycled to the reactor (5) via (12). Part of these go to a thickener (13) in which we extract a maximum amount of water which is recycled to the reactor (5) via (14), the sludge thickened are disposed of in a landfill (15).

Soluble phosphates are analyzed regularly during biological oxidation operations and 15 days after the treatment of the last effluent (No. 8) in the releases (11) from the biological station.

Sur ce graphique :

P désigne la teneur en phosphates exprimée en mg/l,
J designe la durée des opérations en jour,
les astériques correspondent aux injections des effluents à traiter,
la ligne portant des carrés noirs désigne les phosphates totaux,
la ligne portant des carrés blancs désigne les phosphates solubles.

The single graph below shows the results obtained.

On this graph:

P denotes the phosphate content expressed in mg / l,
J designates the duration of operations in days,
the asterisks correspond to the injections of the effluents to be treated,
the line with black squares designates the total phosphates,
the line with white squares designates soluble phosphates.

By carrying out a phosphorus assessment on the biological station we find about 70% of the phosphorus in the aqueous discharge, the rest being entrained by sludge sent to the landfill.

We also did not observe any impact on the functioning of the biological station.

Claims (11)

1. Process for the disposal of waste formed during the manufacture, packaging and use of phosphorus polysulphides, characterized in that it comprises:

   dissolving the said waste by alkaline attack,

   collecting the various solutions obtained in a holding tank, and

   biologically oxidizing the solutions thus obtained, maintained at a pH greater than 7, containing thiophosphates of formula Me₃PS_xO_4-x, in which

   Me represents NH₄ or an alkali metal such as Na or K and

   x is an integer ranging from 1 to 4, phosphates, sulphides and phosphites, before discharge in the form of a solution composed essentially of sulphates and phosphates.
2. Process according to Claim 1, characterized in that the phosphorus polysulphide is P₄S₁₀.
3. Process according to Claim 1 or 2, characterized in that the alkaline attack on the waste is carried out with a sodium hydroxide or potassium hydroxide solution or an ammonia solution.
4. Process according to Claim 3, characterized in that the alkaline solution is a sodium hydroxide solution.
5. Process according to Claim 4, characterized in that the sodium hydroxide solution has a concentration by weight of sodium hydroxide (NaOH) of between 5% and 30% and, preferably, between 10% and 20%.
6. Process according to any one of Claims 1 to 5, characterized in that the waste is introduced into the alkaline solution with stirring at a temperature of between 20°C and 80°C and, preferably, between 25°C and 60°C.
7. Process according to Claims 1 to 6, characterized in that the alkaline solutions collected are sodium hydroxide solutions.
8. Process according to Claim 7, characterized in that the sodium hydroxide solutions are composed essentially of sodium thiophosphate of formula Na₃PS_xO_4-x, in which x is an integer ranging from 1 to 4, of Na₂S, of sodium phosphates and of sodium phosphites.
9. Process according to either of Claims 7 and 8, characterized in that the sodium hydroxide solutions are introduced into a reactor containing activated sludges composed of microorganisms and of bacteria moving about in aerobic medium.
10. Process according to Claim 9, characterized in that the activated sludge reactor is fed with air.
11. Process according to any one of Claims 1 to 10, characterized in that the waste is discharged in the form of a solution containing sulphates and phosphates.

Images