DE4241559A1 - Increasing effectiveness of pptn. of radium@ from mine water - contaminated with uranium@ and fission prods., by addn. of solid contg. barium chloride, improving rate of sedimentation - Google Patents

Abstract

The effectiveness of the pptn. of Ra from mine waters contaminated with U and its natural fission prods. is increased by addn. to the radioactive contaminated water of a solid of particular nature, contg. BaCl2 in moist state. The solid is a residue, freed from water- and acid-sol. components, pref. from lithopone and blanc fixe prodn.. It contains as main component BaSO4, pref. of particle size below 45 microns. ADVANTAGE - The process is cheap and simple, and removes U, As and Ra. The Ra content of water can be lowered from above 5000mB g/l to below 100mB g/l. The microscopic and macroscopic flakes formed on pptn. are loaded and settle in reasonable time in a technically suitable container (up to 10,000 cubic m. vol.), giving purified water with reduced content of Ra and filterable matter. RaSO4 is less water-soluble than BaSO4 (RaSO4 is 4.3 x 10 power(-11) mol/l; BaSO4 is 10 power(-10) mol/l), and Ra is bonded onto the BaSO4.

Description

Uranium ore mining leaves a large number after the decommissioning Sources of waste water, mainly from uranium in the natural Ratio of its radionuclides, the decay products of uranium like Radium and thorium but also due to toxic heavy metals such as Arsenic are contaminated.

The processing residues and production solutions of uranium ore processing are deposited in sedimentation tanks. From this paragraph after the processing plants have been decommissioned Removed pool water, freed of water pollutants and be repelled into the hydrographic network. The volume of this Content water can be several million cubic meters.

Furthermore, the konta emerging at the foot of the sedimentation basin fall mined leachate, which is usually collected by Schad substances are released and released into the hydrographic network.

In the same way must with the drainage of the sludge zone the settling basin of contaminated water with the collected surface waters of contaminated plants, with the accumulation of contaminated groundwater Water as well as with the decontamination of plant parts, Soils, contaminated water.

These waters have to be released into the hydrographic network decontaminated, d. H. of their environmentally harmful ingredients be freed. There are depending on the requirements wastewater quality different methods.

Should only remove the radioactive and / or toxic heavy metals are usually removed using felling methods.  

Are also the salts of soluble ions such as chlorides or sulfates that occur in these waters with considerable levels eliminate, is the use of membrane separation processes in Combination with evaporator systems necessary. Large fall here Amounts of pollutant-containing, soluble salts in a Underground landfill must be spent. The so cleaned In this case, water is of drinking water quality.

The methods of precipitation of radioactive or toxic Heavy metals from the available waters are generally known.

Uranium is mostly made with calcium hydroxide by increasing pH like. That in the form of uranyl carbonate or uranyl sulfate plexes of uranium contained in water fall as water-insoluble Diuranate. In this way, uranium levels are purified Water less than 0.1 mg / l achievable. The precipitated uranium remains in the alkaline medium insoluble in water. The precipitation products are in the former sedimentation basin for the uranium processing mountains.

It is known that freshly precipitated ferric oxide hydrate has specific adsorption capacity for arsenic compounds.

Dosing soluble iron III compounds to the arsenenthal water, iron III oxide hydrate precipitates and adsorbs it Arsenic irreversible. If iron II salts are added, one is Oxidation of iron with calls or other oxidizing agents Iron III oxide hydrate required. With the help of this procedure arsenic contents in the water to be cleaned are less than 0.06 mg / l reached. The resulting, water-insoluble precipitation products are also separated into the former sedimentation basin for the uranium processing mountains.  

The removal of radium from uranium-containing solutions can be done using an ion exchange resin take place (EP 0071810). This requires that the radium-containing solution is contacted with a resin. The Resin must be regenerated or disposed of after loading with radium become. The same applies to the radium enriched in the regenerate. The technical / technological equipments of this process are extremely complex in the treatment of large volume flows. In addition, the regeneration of the ion exchanger Salt loads introduced into the water cycle.

Another known procedure for the separation of radium from uranium-containing solutions is the addition of organic complex forming reagents such as EDTA (US 4,654,200) or D2EHPA (DAPEX process) (US 4,454,097) into that of radium to reini solution. The procedure corresponds to a conventional one liquid-liquid extraction. Design large amounts of water Processes technically / technologically very complex. There is also here also the regeneration and disposal problems. Residual amounts of the organic liquid remain in the cleaning water (solution), since the degree of separation is never 100% can be.

It is also known that the precipitation of radium can be achieved by adding orthophosphate-containing solution to form a relatively stable precipitate (US 4,536,034). The solubility of the precipitates obtained in water is very low, but significantly higher than that of Ba (Ra) SO ₄ .

In US 4,431,609 and DE 34 02 700 it is proposed to use radium Contacting the solution to be cleaned (or the water) with Remove coal fly ash. The clarification of larger volume flows causes considerable due to the fineness of the solid technical / technological effort and is technical, even under Addition of organic flocculants, difficult to control.  

Used to precipitate the radium from uranium mining waters usually water-soluble barium salts, in particular Barium chloride (US 4,423,007). Here you take advantage of the fact that radium, due to its position in the periodic table, corresponds to barium always has similar chemical properties and the named water contain dissolved sulfates.

The radium sulfate is less water-soluble than the barium sulfate

(Solubility products: BaSO ₄ = 1 · 10 ^-10 mol / l;
RaSO ₄ = 4.3 · 10 ^-11 mol / l).

For this reason, the binding of the radium to the Sulfate.

Since the wastewater from the uranium industry always has higher sulfate contents, the barium added as chloride, including the radium contained in the water, precipitates as Ba (Ra) SO ₄ .

Untreated water can contain more than 5000 mBq / l radium.

By treating this water with BaCl ₂ , the radium content can be reduced to less than 100 mBq / l.

In practice, the removal of the precipitated pollutants from the water.

The Ba (Ra) SO ₄ particles are generally smaller than 1 µm and have an extremely slow settling rate.

Precipitation of the arsenic with water-soluble iron salts also produces large-volume iron oxide hydrate flakes, some of which include the Ba (Ra) SO ₄ particles. Due to their low density, the flakes float in the water to be cleaned.

By adding organic flocculants large-volume flocculation aggregates are formed, but due to their low inherent density and the low solids density of the precipitated hydroxide particles they also have a very low sinking rate. Due to the extremely low mass of the barium (radium) sulfate formed, which has a high solid density (c = 4.2 mg / m ³ ) but an extremely small particle size (<1 µm), the sinking rate is only marginally affected.

If the precipitation takes place, as usual, in an alkaline medium, fractions of free acid in the iron or barium salts used for the precipitation lead to the formation of microbubbles (predominantly CO ₂ ), which adhere to the Ba (Ra) SO ₄ or iron oxide hydrate particles retire. If these particles are attached to the flocculant molecules, in the worst case the flocs formed can float in the purified water (flotation effect).

Technically, large amounts of water of several hundred cubic meters per hour can only be treated economically in large containers (thickeners up to 10,000 m ^{3 in} volume).

The solid substances sediment and become by filtration further treated or in the thickened state in the fine sludge zone of the sedimentation tanks.

If the flocculated pollutants float in the thickener, with the purified water in the receiving water and place new represents an environmental hazard.

For this reason, the cleaned waters are a control subjected to filtration and given over filter units, which the Separate any remaining suspended matter later (gravel bed filters, candle filters, etc.). Gravel bed filters have to be which depends on the content of suspended matter in the water become. If there are large amounts of solid substances in the water, the term of the aggregates mentioned shortens between Backwashing phases considerably and more personnel and apparatus technology Effort increases in a way that is no longer manageable.  

The noticeable improvement of the described defect brings Use of contact sludge processes when cleaning solids contaminated water. An experimentally determined amount of sedimented material (so-called old sludge) is called a suspension separated and returned to the raw water to be cleaned. The solid particles are incorporated into the flakes and formed increase the sink rate of the flake aggregates formed.

This is a prerequisite for using this method Presence of a sufficient amount of suitable solid Particles in the raw water to be cleaned. In the cleaning leading waters is usually not the condition mentioned given.

The generation of a solid substance suitable for problem solving is as low as possible due to the required fineness Fine grain fraction with great effort for grinding and Classification linked so that the economy added an extra of solid material specially prepared for this stage of the process excludes.

The effect is further reduced by the fact that conventional solid substances have a maximum density of 2.7 mg / m ³ , that is to say the difference in driving force from buoyancy and gravity is relatively small.

So far, there is still a technical deficiency described none practically realizable with reasonable economic effort bare solution.

The invention has for its object to develop a method that weighs the multitude of microscopic and macroscopic flakes formed so that they settle in the technically feasible container volume (up to 10,000 m ³ ) available with certainty on the ground and can be endured from the overflowing, purified water.

The object is achieved in that Increasing the effectiveness of the precipitation of radium with uranium and its natural decay products contaminated mining A solid with a certain quality is added to water which contains barium chloride in its moisture.

The following conditions must be met to solve the problem the following are required:

• - The water to be cleaned must have a finely divided solid be added in sufficient quantities
• - The solid particles must be as high as possible Have solid density,
• - The solid must be inexpensive in sufficient quantity To be available,
• - The solid itself must not be in the one to be cleaned Water soluble water pollutants such as soluble salts or Contain heavy metals.
• - The solid must adhere to the flake aggregates formed accumulate or be surrounded by the flakes.

The solid to be used becomes the residue of the litho pone and Blanc fixed production produced as follows:

The water- and acid-soluble components of the solid material mentioned are removed during the decontamination. The remaining solid essentially consists of water and acid-insoluble, finely divided BaSO ₄ (approx. 50%), slag and / or coke residues (approx. 40%) and silicate residues, which are involved in the roasting of the heavy spade in the process of the former Lithopone - and Blanc fixe production remained (approx. 10%).

The solid can correspond to the actual decontamination treated according to the further intended purpose in two ways become:

• a) By washing on the press filter with water. A decontaminated solid is formed, which is on a Class II or III landfill can be landfilled.
• b) by dispensing with the washing stage. The BaCl ₂ still contained in the filter cake is used to precipitate the radium from the radium-containing water to be cleaned.

The decontaminated solid residue is separated from the solution using a press filter. This creates a firm, dry-acting filter cake with a moisture content of approx. 25%. The moisture contains the content of BaCl ₂ that can be used for radium precipitation. The solid residue is easy to transport due to its firm, stackable consistency.

Before using the supplied material to precipitate the radium, a suspension with a known concentration of BaCl ₂ must be prepared in the liquid phase.

For this purpose, the solid filter cake, corresponding to the concentration of the BaCl ₂ in the moisture (determined analytically on delivery), is added to a stirred tank in which there is a pre-calculated volume of water.

The suspension is usually added to the contaminated water to be treated, analogously to the existing practice of adding commercial BaCl ₂ solution, in the pipeline in front of the sedimentation apparatus or in a special suspension container in proportion to the quantity. The regime of adding calcium hydroxide (pH adjustment), soluble iron salts (e.g. FeCl ₃ ) to precipitate arsenic and a polymeric flocculant is not affected by the addition of BaCl ₂ in the form of a suspension.

The weighted flakes settle in the sedimentation apparatus off the ground. This thin sludge can be removed, possibly soluble Components stabilized with calcium hydroxide and over Pipes are pushed off into the settling tanks.

Made from natural uranium and its natural decay products Water from the sedimentation apparatus flows into the receiving water or carried out in apparatus for control filtration.

With the aid of the method according to the invention, several can be significant technological and economic advantages with each other unite in the interaction between:

• - the simplification of the decontamination technology of the solid, pollutant-containing stockpile material,
• - the commercially obtainable that can be obtained from it Value products,
• - And the use of the generated residual material as a valuable material in the precipitation of radium from reject water lie.

There is a so-called synergy effect, which is favorable Case the technological cost of decontamination of the product residues and to save costs when recycling the generated residual material leads.

The listed significant technological and economic advantages parts of the recovery of the decontamination of the production residues generated residue for the precipitation of radium from the Contaminated water from mining facilities consists of:

• a) the saving of the decontaminated solid necessary landfill space on a household waste or industrial area landfill and saving the necessary costs.  
• b) the more economical design of the technological process decontamination of production residues due to elimination the last washing stage.
• c) the elimination of the costs for the commercial BaCl ₂ for the precipitation of the radium from the contaminated waters.
• d) the weighting of the flake aggregates formed in the purification of the waste water from uranium, arsenic and radium by the BaSO ₄ particles from the solid of the filter residue and thus improvement of the quality of the waste water with regard to the radium and suspended matter content.
• e) the additional long-term effectiveness of the finely divided BaSO ₄ contained in the solid used to approx. 50% with regard to the absorption / incorporation of radium from the pool water after storage of the residue in the settling tank of the operator of the system for cleaning the contaminated water from radioactive components.
• f) in the free provision of solids for Filling the trough in the sedimentation basin to displace the Pool free water before the final contouring of the above-mentioned systems.

The specified synergy effects remain under the condition economically effective that the distance between the location of the Decontamination of the tailings residue and the location of the Ein a set of decontaminated solid for radium precipitation Transport possible.

With the help of the method according to the invention, a product can be Residual residue, preferably the Lithopone and Blanc fixed products tion using a synergy effect between the operator decontamination technology and the customer of the residual material the decontamination, which consists of:

• - through the commercial sales of decontamination accumulating materials at the operator of the decontamination technology as well
• - the cost-saving use of the decontamination residue tion of the production residues, preferably the Lithopone and Blanc fix production for the precipitation of the radium from reject water Mining systems of uranium production without use of landfill space at a municipal waste disposal site for the user of the resulting residue the technological costs of Decontamination can be covered.

An exemplary embodiment is shown and explained below:

In an experiment, a radioactive contaminated water from the sedimentation basin of a former uranium processing plant is to be cleaned of uranium and radium. The precipitation of the radium is carried out using equivalent amounts of BaCl ₂ in the form of a commercial barium chloride solution and in the form of a filter residue from the decontamination of a solid sample of a production residue from the Lithopone and Blanc fixed production, which was decontaminated in accordance with the intended technology.

The waste water to be cleaned should be that shown in Table 1 Possess composition.

Table 1

Composition of the waste water to be cleaned by radium

The decontaminated residue used to precipitate the radium the Lithopone and Blanc fix production continues like in Tabel le 2 shown together.  

The comparative tests were carried out according to the ones shown Schemes:

Scheme 1

Use of commercial barium chloride for radium precipitation

Scheme 2

Use of the barium chloride-containing residue obtained from the decontamination of the production residue of the Lithopone and Blanc fixed production for radium precipitation:

The specific consumption of the reagents (values in brackets behind the reagents) refer to one liter to clean of the water.

The commercial BaCl ₂ solution was added to the conventional technology according to the reject water.

Table 2

Solid and eluate after elution according to DEV S4

The filter residue containing BaCl ₂ contained the moisture provided for in decontamination technology and the corresponding BaCl ₂ content. One of the specific BaCl ₂ addition amount corresponding mass of the filter cake was suspended in the moist state in 10 ml of water and this suspension added to the shock water to be treated.

The results of the experiment are shown in Table 3:

According to the conventional and according to the Ver water cleaned according to the procedure is shown in Table 3 established differences in the radium content after precipitation.

Table 3

Composition of the water cleaned from radium according to the conventional and the inventive cleaning technology

It can clearly be seen that the radium content after the precipitation with the BaCl ₂ -containing filter residue is lower than with the commercial BaCl ₂ .

Claims (4)

1. A method for increasing the effectiveness of the precipitation of radium from uranium and its natural decay products contaminated th mining water, characterized in that the radioactive contaminated water is added to a solid with a certain nature, which contains BaCl ₂ in its moisture. 2. The method according to claim 1, characterized in that as a festival a substance from other water- or acid-soluble stocks share liberated residue, preferably from the Lithopone and Blanc fixe production is used. 3. The method according to claim 1, characterized in that the solid material contains as the main component finely divided BaSO ₄ , the particle diameter is preferably less than 45 microns. 4. The method according to claim 1 and 3, characterized in that the BaSO ₄ -containing solid is stored after the Ra precipitation in the sludge zone of the sedimentation tank to be rehabilitated for the residues of the uranium ore preparation.