RU2339906C1 - Method of solid fuel rocket engine hydro-cavitating wash-out drains treatment - Google Patents

Abstract

FIELD: technological processes; chemistry.

SUBSTANCE: method of treatment of drains from hydro-cavitating wash-out of mixed solid rocket fuel charge on the basis of ammonium perchlorate from solid fuel rocket engine includes supply of high-pressure liquid from closed water circuit into wash-off hydro-cavitating installation, preparation of drains in the form of suspension that contains solid phase from destroyed charge of solid fuel and liquid of closed water circuit, separation of suspension solid phase from liquid of closed water circuit, accumulation of solid phase doses and reverse osmosis treatment of closed water circuit liquid from ammonium perchlorate. From accumulated doses of solid phase ammonium perchlorate is leached at increased temperature in several leaching reactors of periodic action. Every following accumulated dose of solid phase is loaded into the following leaching reactor of periodic action, and the following components are supplied as produced after leaching of ammonium perchlorate from previous dose of solid phase and evaporated for balancing of water content: mother water and concentrate with provision of necessary concentration of solution in reactor.

EFFECT: ecological purity of rocket engine charges liquidation process.

5 cl, 1 ex, 1 dwg, 1 tbl

Description

The invention relates to the field of disposal of military equipment and can be used in environmentally safe and resource-saving disposal of solid propellant rocket engines (solid propellant rocket engines) and mixed solid propellant rocket charges (SRTT) based on ammonium perchlorate (PCA) as an oxidizing agent by hydrocavitational washing out of SRTT charges from RDTT cases in the form of an aqueous suspension of charge destruction material. The advantage of leaching is the process safety, including when working with defective CPTT charges. A common drawback of works related to ammonium perchlorate is the danger of its release into the environment and its spread over open and underground waterways over long distances with pollution of water bodies and groundwater. Therefore, all work with PHA should exclude the discharge of waste into sewer systems and the environment.

Known methods for processing materials of destruction of charges of SRTT, aimed at the regeneration and recycling of PCA from large fragments of SRTT obtained by the destruction (cutting) of charges. According to the PHA extraction or leaching method, the SRTT removed from the solid propellant was cut into small pieces that were leached in water. However, due to the sticky nature of CPTT, large CPTT agglomerates were obtained that prevented the necessary mixing of water with fuel, which is required for efficient extraction of the oxidizing agent. To recover more than 25-30 wt.% Of the available oxidizing agent, the agglomerated fuel required continuous grinding and cutting in a leach solution. This required a large expenditure of time and energy for the operation of the cutting tool during the extraction of PHA [1].

An improved process has also been proposed for extracting fuel ingredients from fuel waste, which is economical, energy-saving and environmentally friendly. The extraction of the oxidizing agent in accordance with this patent for the invention is carried out in an aqueous leachable suspension containing additives that modify the surface of the fuel, thereby eliminating the agglomeration of the fuel during cutting and the suspension of particles in water is allowed. The result is the rapid dissolution of PCA and its subsequent separation from the fuel residues by filtration or decantation of liquids. PCA is removed from the filtrate by cooling and filtering precipitated PCA. The resulting PCA depleted solution is recycled to further extract the PCA from another portion of the fuel.

Fuel agglomeration is prevented by the addition of a surfactant that is adsorbed on the surfaces of the binder, reducing the sticky nature of the exposed surface. The energy required for mixing fuel suspended in water was less than 1/50 of the energy required for mixing pyrotechnic materials having wet, sticky agglomerated fuel and not containing a dispersing agent [2].

A common disadvantage of the known methods as applied to the problem being solved is the lack of a connection between the process of washing the fuel out of the solid propellant rocket hull and treating the effluent in the form of a very dilute suspension, which corresponds to the technology of the fuel destruction process, which requires a flow rate of 50-80 l of water per 1 kg of extracted fuel. Concentration of PCA leached in such a suspension can be very energy-intensive and available only in several ways, such as evaporating water and freezing water. The price of such concentration with subsequent incineration can be up to 95 and 50 dollars / m ³ , respectively. In addition, in the process of washing the fuel, the entry of PCA into the closed loop water used to power the hydrodynamic destructive devices should be taken into account. This water needs periodic cleaning from PHA so that there is no change in destructive properties.

The closest in technical essence and adopted for the prototype is a method implemented in a mobile installation for hydro-jet cleaning of the body of a rocket engine of solid fuel, according to which solid materials washed out by high pressure water in the form of a suspension are removed from the body through the mass pipe of the collector connected to the open end of the cleaned object. Using the mass line, the entire washed suspension is sent to a collection tank for settling. The liquid phase is taken from the upper part of the receiving tank, cleaned in hydrocyclones and filters, after which it is fed into the bulk tank and then the pressure tank and then to the high pressure pump. Thus, create a closed loop of leaching water. The closed loop is fed with clean water. Water is taken from the closed loop for reverse osmosis desalination, and then the desalinated water is returned to the closed loop, and the resulting concentrated liquid phase is taken to a liquid concentrated phase storage tank for further loading into transportation containers and sending for processing. The solid phase concentrate from hydrocyclones and from the lower part of the receiving tank is collected in a dense-phase suspension accumulator equipped with a diaphragm pump for unloading it into shipping containers and sending it for processing [3].

The disadvantage of the processing method adopted as a prototype is the incompleteness of the processing process, which should be linked to the work and technological equipment of other enterprises, which includes a number of organizational and technical problems. During transportation and transshipment operations, there is a possibility of environmental pollution as a result of spills of PHA solutions. The reverse osmosis desalination should be subjected to the entire volume of water in a closed circuit, into which all soluble materials from SRTT have passed. This increases the load on the reverse osmosis installation, which should have three stages of cleaning with a maximum pressure of more than 7.25 MPa.

The technical problem solved by the present invention is the treatment of effluents from hydro-cavitation leaching of solid propellant rocket rocket materials in the form of an aqueous suspension of the solid phase of CPTT fracture materials to the final products - crystallized PCA, water and aluminum oxide without removal from the system to the environment or sewage of any liquid media.

The solution of the technical problem was achieved by the fact that in the method of treating wastewater from hydro-cavitation leaching of a mixture of solid rocket fuel based on ammonium perchlorate from a rocket engine of solid fuel, which includes supplying high-pressure liquid from a closed water circuit to a wash-out hydro-cavitation installation, obtaining effluents in the form of a suspension containing the solid phase from the destroyed charge of solid fuel and the liquid of the water circuit, I will close the separation of the solid phase of the suspension from the liquid of the water circuit, the accumulation of doses of the solid phase and reverse osmosis purification of the liquid of the closed water circuit from ammonium perchlorate, the separation of the solid phase of the suspension from the liquid of the closed water circuit is carried out continuously immediately after its formation, ammonium perchlorate is leached from the accumulated doses of the solid phase at elevated temperatures in several leaching reactors batch action, for which the first accumulated dose of the solid phase is loaded into the first batch leach reactor and feed t of liquid from a closed water circuit to obtain the required concentration of the solution in the reactor, ammonium perchlorate is leached, then solid insoluble leach waste and ammonium perchlorate solution are separated, dried solid insoluble leach waste and destroyed, crystallization of the ammonium perchlorate solution is carried out by lowering the temperature of the solution, separating the obtained crystalline ammonium perchlorate from the mother liquor and dry it, the separated mother liquor and the concentrate obtained at osmotic purification of a liquid of a closed water circuit from ammonium perchlorate, evaporated to balance it by water content, water obtained by condensation of steam from drying solid insoluble leachate and crystalline ammonium perchlorate from the evaporation of the mother liquor and from the evaporation of the concentrate obtained by reverse evaporation purification of the liquid of a closed water circuit from ammonium perchlorate, each subsequent accumulated dose of the solid phase is loaded into the next reaction Op leaching and fed batch obtained after leaching of ammonium perchlorate previous dose solid phase evaporated to balance the water content of the mother liquor and concentrate to obtain the required concentration of the solution in the reactor. A dose of a solid phase corresponding to 100-150 kg of solid fuel is accumulated per liquid revolution in a closed water circuit. Each dose of the solid phase is accumulated during each revolution of the liquid of the closed water circuit. The separation of the solid phase of the suspension from the liquid of the closed water circuit is carried out on filters, in a centrifuge or in hydrocyclones. Solid, insoluble leachate is disposed of by incineration with the capture of harmful gaseous wastes.

A comparative analysis of the essential features of the prototype and the proposed method shows that the distinguishing features of the proposal are those in accordance with which:

separation of the solid phase of the suspension from the liquid of the closed water circuit is carried out continuously immediately after its formation;

ammonium perchlorate is leached from the accumulated doses of the solid phase at elevated temperature in several batch leaching reactors;

the first accumulated dose of the solid phase is loaded into the first batch leach reactor and liquid is supplied from a closed water loop to obtain the necessary concentration of the solution in the reactor;

the separated mother liquor and concentrate obtained during reverse osmosis purification of the liquid of the closed water circuit from ammonium perchlorate are evaporated to balance them with respect to water content;

water is withdrawn into the closed loop from steam condensation from drying solid insoluble leachate and crystalline ammonium perchlorate from evaporation of the mother liquor and from the evaporation of the concentrate obtained from reverse osmosis purification of the liquid of the closed water loop from “ammonium perchlorate;

each subsequent accumulated dose of the solid phase is loaded into the next batch leach reactor and the obtained after leaching ammonium perchlorate from the previous dose of the solid phase evaporated to balance the water content of the mother liquor and concentrate to obtain the required concentration of the solution in the reactor.

The invention will be more clear from a consideration of the drawing, which presents a block diagram of the movement of mass flows between devices, and from the following description of an example embodiment of the invention.

As shown in the drawing, the method of treating wastewater relates to a washing unit 1, the destruction of the SRTT in which is carried out using high-pressure water entering it through line 2 from group 3 of water treatment apparatuses. Group 3 includes filters for trapping fine impurities, high pressure pumps, pressure tanks, water storage tanks, heat exchangers, valves and other elements necessary for the functioning of the water circuit. Further, the water circuit contains a mass pipe 4 from the washing unit 1 to the first separator 5. The first separator 5 is designed to separate the solid phase of the destroyed SRTT from the water from the PCA, which entered it during the destruction of the charge. The water circuit is closed by line 6, having a branch line 7 to the reverse osmosis installation 8 for purification of water from PHA. The purified water flows back to the closed water circuit via line 9. The PHA concentrate from the reverse osmosis unit is withdrawn via line 10 to the evaporator 11. The separator 5 has an outlet for the solid phase to the transport bucket 12 to accumulate a dose of the wet solid phase. Using a ladle 12, a dose of a solid phase is transported to a receiving funnel 13 of one of the batch leaching reactors 14. The number of reactors 14 is determined by the mass of leached solid fuel charge, the time of leaching of the solid phase in the reactor, the time of liquid circulation in a closed water circuit, and the dose accumulation time. It is preferable to have equal times of fluid turnover and dose accumulation. On line 15, the batch reactor 14 is connected to the evaporator 11 of the mother liquor from the crystallizer and concentrate from the reverse osmosis unit 8. The batch reactor 14 is equipped with a paddle mixer and a heating jacket. The output of the periodic leach reactor with a heated flexible hose 16 is connected to a receiving funnel of the second separator 17. The heated second separator 17 is designed to separate solid insoluble leachate and concentrated PHA solution. The solid insoluble leachate from line 18 is discharged into the dryer 19, preferably with hot air in a suspended layer mode. The hot concentrated PHA solution is sent through line 20 to crystallizer 21. The crystallizer is equipped with a cooling jacket to lower the temperature of the solution and isolate crystalline PHA. Crystalline PHA along line 22 is taken to dryer 23 and then for packing and shipping to the warehouse. The lines 24, 25 and 26 of the dryer 19 and 23 and the evaporator 11 are connected to a condenser 27, the output of which is connected by a line 28 to a group 3 of water treatment apparatuses. Line 29 with a point of supply of concentrate from the reverse osmosis unit 8 along line 10, the mold 21 is connected to the evaporator 11.

Example. In accordance with the project, a hydro-cavitation flushing unit is designed to remove SRTT charges from solid-state rocket engines with a diameter of 300 mm. CPTT consists mainly of 80 wt.% PCA and 20 wt.% Aluminized fuel binding agent (HS). High pressure water flow rate is about 8 kg / s. Since the specific consumption of water for leaching is at the level of 50-80 kg / s per 1 kg of fuel, then at such a rate, the productivity of erosion of the fuel is 0.1 kg / s. On the surface of the end face of the charge can be located up to 8 jet nozzles leaching. The number of jet nozzles is limited by the permissible power of high pressure pumps, since the specific energy consumption for leaching is 2-3 MJ / kg of fuel, depending on the mechanical properties of the fuel. For 1000 s, 100 kg of STRT is washed out, which together with the water necessary for leaching PHA will amount to 150-200 kg, depending on the final concentration of the solution. From the washing-out hydro-cavitation installation 1 along line 4, an aqueous suspension from the solid phase of the destroyed charge and the liquid of the closed water circuit enters the first separator 5. The solid phase of the destruction materials is continuously separated from the liquid of the closed water circuit, for example, on a filter, in a centrifuge, in a hydrocyclone or in other device. The accelerated separation of water from the solid phase reduces the entry of PHA into the liquid of the closed water circuit, reduces the load on the reverse osmosis water treatment plant and increases the yield of PHA. For a dose equivalent to 100 kg of STRT, for one revolution of water in a closed water circuit, a volume of liquid in a closed water circuit of about 8000 kg is required. According to the results of experiments, it is known that when the charge is destroyed, about 20% of the PCA from the extracted STRT enters the closed loop liquid. In this case, in the transportation bucket 12 receive the first dose of the solid phase composition:

PHA 64 kg HS 20 kg Water 84 kg PHA received with water 0.168 kg

To obtain a solution with a saturated concentration of PHA of 600 g / kg of water in the reactor, it is necessary to have 106.95 kg of water. For the first dose of the solid phase, additional water in the amount of 22.95 kg with a PHA content of 0.046 kg is taken from the closed water circuit through the separator 5. The first dose of the solid phase and water are loaded into the first reactor 14-1. Using instruments, the concentration of PHA in the liquid of the closed water circuit and the mass of the dose of the solid phase are monitored. The reactor 14-1 is heated to approximately 65 ° C and the contents are intensively mixed. The concentration of PCA in a saturated solution at a temperature of about 65 ° C is approximately 600 g / kg of water. The water content in the solid phase may differ from the calculated (50:50) and deviations are taken into account when calculating the added water.

After leaching for 30-40 minutes, the heated mixture is fed through a heated hose 16 to a second separator 17, in which a hot concentrated PHA solution is separated from solid insoluble leachate waste in the form of a composition product:

HS 20 kg Water 20 kg PHA from a concentrated solution 12 kg

Separated solid insoluble leachate from line 18 is sent to dryer 19, preferably by heated air in a suspended layer mode. The dried solid insoluble leachate is fed to an incinerator (not shown). When washing from PHA, the combustion of the gas becomes less intense and will require a greater consumption of air and combustible gas. Water vapor from the dryer 19 is diverted to a condenser 27 for subsequent supply of condensed pure water to a closed water circuit through a group of 3 water treatment apparatuses.

A hot concentrated PHA solution from the second separator 17, containing 52.214 kg of PHA in 86.95 kg of water, is fed through line 20 to the crystallizer 21, where, after the PCA solution arrives, the temperature is lowered from 65 ° C to 10-15 ° C. The released and precipitated wet crystalline PHA in the amount of 44.962 kg together with water 39.097 kg is separated and sent to line dryer 23 through line 22. The obtained dry crystalline PHA is packed and taken to a warehouse for storage on demand. The water vapor formed during drying is discharged via line 25 to a condenser 27 for subsequent input of the pure water obtained by condensation into a closed water circuit through a group of 3 water treatment devices. The mother liquor remaining in the crystallizer 21 with a PHA concentration of 150 g / kg of water is connected through a tee on line 29 to the concentrate obtained from the reverse osmosis unit and evaporated to the water content required for operation of the next batch leach reactor 14-2.

The periodic leaching reactor 14-2 after the second turn of the closed loop water is loaded with the contents of the transportation bucket 12 of the composition:

PHA 64 kg Aluminized Fuel Binder 20 kg Water 84 kg PHA from closed loop water 0.336 kg PHA from the mother liquor 7.178 kg

In total, 71.514 kg of PHA is charged into a batch reactor 14-2. To obtain a leached solution with a concentration of 600 g / kg of water, 119.19 kg of water will be required. If there are already 84 kg of water in a dose of the solid phase, 35.19 kg of water of the mother liquor must be added. Evaporation in the evaporator 11 of the initial mother liquor containing 7.178 kg of PHA in 47.853 water to a water content of 35.19 kg gives a solution containing 204 g / kg of water, which is also loaded into the reactor 14-2. The vapor formed during evaporation along line 24 is taken to a condenser 27 and then along line 28 to be introduced into a closed loop through a group of 3 water treatment apparatuses.

During the first few revolutions, the liquid of the closed water circuit does not turn on the reverse osmosis unit, since the concentration of PCA in the circuit is very low, at a level of less than 1%. The intake of pure water from steam condensation at the level of 76 kg has little effect on the concentration of PCA in the mass of the liquid in the closed water circuit of 8000 kg.

Recycling of the mother liquor became possible due to the addition of water after the first revolution from a closed loop to reactor 14-1.

The separation of the liquid of the closed water circuit from the solid phase of the effluent immediately after its formation provides a reduced intake and accumulation of PCA in the liquid of the closed water circuit. Due to this, the requirements for the operating modes of the reverse osmosis treatment plant are reduced. The reverse osmosis unit should have a performance reserve to compensate for possible abnormal jumps in PCA concentrations resulting from structural changes in the washed away SRTT charges, for example, the appearance of cracks, delaminations, breaks, and other defects that, when washed out, increase the contact surfaces of the SRTT with the liquid by maintaining concentrations PCA in a liquid of a closed water circuit at a level acceptable for the effective washing out of SRTT. This allows you to save the specified continuous technological process of leaching the charge STRT.

In the normal mode of reduced accumulation of PHA, reverse osmosis cleaning is carried out according to the need to remove the accumulated PHA, for which a part of the nominal productivity, equivalent to a part of the liquid volume of a closed water circuit, is sufficient. A portion of the fluid selected from the reverse osmosis purification loop may correspond to the volume of fluid separated from the suspension of the accumulated dose of the solid phase. Since the reverse osmosis plant has high energy consumption, its partial use reduces operating costs and reduces the cost of disposal of solid propellant rocket motors.

With a mass of SRTT in solid propellant rocket motor less than 1000 kg, the inclusion of a reverse osmosis unit is not required, the concentration of PCA in a closed water circuit in the limiting case will increase to 2%. The cleaning is carried out in the period between the removal of one solid propellant solid propellant and the setting for washing out another solid propellant solid propellant. The resulting concentrate is added in parts to the leach reactors, each time balancing the water content added to the leach reactor.

In other cases, with the washing away of the SRTT charges of a larger mass, it is preferable to perform reverse osmosis cleaning after every fifth water revolution in a closed water circuit.

The results of the estimated calculations are summarized in the table. It can be seen that after the start of the effluent treatment process from the initial state, the yield of product PHA quickly approaches a constant value at a level of slightly more than 52.6 kg.

Using instead of periodically separating doses of the wet solid phase, loading the wet solid phase into one drive for the entire charge complicates the subsequent processing of a large mass of material, worsens mixing, and increases the processing time, since the ratio of the heating or cooling area to the internal volume decreases with increasing volume.

An analogue patent [2] claims the use of surfactant additives in leaching reactors to better disperse the solid phase. The experiments on the destruction of the charges of SRTT after decommissioning of solid propellant rocket engines have shown that SRTT after 20 or more years of operation differs in adhesion and mechanical properties from the new SRTT. Destruction materials when in water do not agglomerate and do not envelop on the mixer. The coating is detected only on the surface of the liquid, if there is a floating of the solid phase. Nevertheless, it is permissible to use surfactants specific for each SRTT.

Table Characteristic Sequence number of circulation of water in a closed loop one 2 3 four Loading dose into the reactor along line 13 PHA 64 64 64 64 HS twenty twenty twenty twenty Water 84 84 84 84 PHA with closed loop water 0.168 0.336 0.504 0.672 Loading into the reactor via line 15 PHA 0.046 ^*) 7,178 8.1832 8.3438 Water 22.95 ^*) 35.19 37,1453 37,693 The content of components after separation of the HS on line 18 PHA 52.14 59,514 60.6872 61,0158 Water 86.95 99.19 101,1453 101,693 The yield of crystallized product on line 22 of the composition PHA 39.0974 44,6355 45,516 45.7618 Water 39.0974 44,6355 45,516 45.7618 PHA with water 5,8646 6,6953 6.8274 6.8643 Total: PHA 44,962 51,3308 52,3434 52,6261 The mother liquor at the exit of the mold 21 composition PHA 7,178 8.1832 8.3438 8.3896 Water 47.8526 54.5545 55,6293 55.9312 Evaporation of recycle water: - steam on the lines 24.25.25 76.77 82,0447 83,4523 83,6437 - water supply through line 15 to the next reactor 35.19 37,1453 37,693 38,0493 GS - aluminized fuel-binding agent; PHA - ammonium perchlorate
^*) - loading from a closed water circuit through a separator.

The use of single separators, crystallizers, dryers for the entire series of leaching reactors can increase the utilization rate of these devices.

The concentration of the hot saturated PCA solution is selected in the range from 250 g / kg water to 800 g / kg water. The patent analogue [2] shows the technical applicability for PCA of such an isohydric crystallization method. However, an increase in concentration, and, accordingly, temperature, leads to an increase in heat loss. With a decrease in concentration, the volumes of reactors and other apparatuses increase, which leads to an increase in capital costs.

The closure of the steam drains of the drying apparatus and the evaporator on the steam condenser with the subsequent removal of the obtained water into a closed water circuit allows the PHA aerosols to be released into the atmosphere.

The wastewater treatment method of this proposal is suitable for working with other STRT flushing plants, for example, from larger solid propellant solid propellants with charge masses from 1 to 25 tons. Moreover, the flushing performance will increase slightly due to pump power limitations. In the considered example, the productivity is 360 kg / h. With such productivity, round-the-clock operation will allow to process all effluents from the largest charge of 25 tons in about 70 hours with 252 loadings of doses of the wet solid phase into the leach reactors.

The absence of liquid-phase effluents and the packing of solid PCA in metal drums at the place of its separation allows ensuring the environmental cleanliness of the solid propellant elimination complex without the use of complex and low-productivity methods for treating industrial wastewater such as trapping on ion exchangers, activated carbon, etc.

Information sources

1.US 3451789 (McIntosh)

2. US 4,198,209 (Frosh et al.)

3. RU 2195629, 2002.

Claims (5)

1. A method of treating wastewater from hydro-cavitation leaching of a mixture of solid rocket fuel based on ammonium perchlorate from a rocket engine of solid fuel, comprising supplying a high-pressure liquid from a closed water circuit to a wash-out hydro-cavitation unit, and obtaining wastewater in the form of a suspension containing a solid phase from a destroyed solid charge fuel and liquid of the closed water circuit, separation of the solid phase of the suspension from the liquid of the closed water circuit, the accumulation of doses of the solid phase and Brain-osmotic purification of the liquid of the closed water circuit from ammonium perchlorate, characterized in that the separation of the solid phase of the suspension from the liquid of the closed water circuit is carried out continuously immediately after its formation, ammonium perchlorate is leached from the accumulated doses of the solid phase at elevated temperatures in several batch leaching reactors, for which the first accumulated dose of the solid phase is loaded into the first batch leach reactor and liquid is supplied from closed aqueous circuit to obtain the required concentration of the solution in the reactor, ammonium perchlorate is leached, then solid insoluble leach wastes and ammonium perchlorate solution are separated, solid insoluble leach wastes are dried and destroyed, crystallization of the ammonium perchlorate solution is carried out by lowering the temperature of the solution, the obtained crystalline perch the mother liquor and dry it, the separated mother liquor and the concentrate obtained by reverse osmosis liquid These closed water circuits from ammonium perchlorate, evaporated to balance their water content, divert the water obtained by condensing steam from drying solid insoluble leachate and crystalline ammonium perchlorate from the evaporation of the mother liquor and from the evaporation of the concentrate obtained by reverse osmosis liquid purification closed water circuit from ammonium perchlorate, each subsequent accumulated dose of the solid phase is loaded into the next periodic leach reactor actions and feed obtained after leaching of ammonium perchlorate from the previous dose of the solid phase evaporated to balance the water content of the mother liquor and concentrate to obtain the required concentration of the solution in the reactor. 2. The method according to claim 1, characterized in that the dose of the solid phase corresponding to 100-150 kg of solid fuel is accumulated for one revolution of the liquid in a closed water circuit. 3. The method according to claim 1, characterized in that each dose of the solid phase is accumulated during each revolution of the liquid of the closed water circuit. 4. The method according to claim 1, characterized in that the separation of the solid phase of the suspension from the liquid of the closed water circuit is carried out on filters, in a centrifuge or in hydrocyclones. 5. The method according to claim 1, characterized in that the solid insoluble leaching waste is destroyed by incineration with the capture of harmful gaseous waste.