WO1998013308A1

WO1998013308A1 - Process for the treatment and decontamination of acid waters which contain dissolved metals and their conversion into fertilizers (pidra process)

Info

Publication number: WO1998013308A1
Application number: PCT/ES1997/000231
Authority: WO
Inventors: Manuel Valiente Malmagro
Original assignee: Tecnologias Zero-Red, S.L.
Priority date: 1996-09-24
Filing date: 1997-09-18
Publication date: 1998-04-02
Also published as: AU4302397A; ES2127157A1; ES2127157B1

Abstract

Process for the treatment and decontamination of acid waters which contain dissolved metals and their conversion into fertilizers, comprising the combination of three specific processes: a) selective removal of iron and of the acidity of the medium through biooxidation of Fe (II) and precipitation with alkalis (Ca(OH2), NaOH, KOH or NH4OH) of Fe (III) compounds; b) taking advantage of the high sulphate content of the acid waters for the synthesis, through ionic exchange, of K2SO4 or NH4SO4, free of chlorides which may be used as fertilizers or commercialised in other applications; c) recovery of the metals contained in such waters: Cu?2+, Al3+, Zn2+ and Mg2+¿. The process may be applied to acid waters originating from various sources: active or inactive mine installations, river basins, water courses, lagoons, etc. which, due to their contact with numeral masses, are contaminated with sulphuric acid and heavy metals, as well as industrial plants which produce acid effluents (for example galvanotechnical industry).

Description

PROCEDURE FOR THE TREATMENT AND DECONTAMINATION OF ACIDED WATERS CONTAINING DISSOLVED METALS AND THEIR CONVERSION IN FERTILIZERS (PIDRA PROCESS). OBJECT OF THE INVENTION The invention object of the present report refers to an ecologically clean procedure for the integrated treatment and decontamination of acidic waters (Integral Process of Decontamination and Recovery of Acidic Waters (PLDRA Process)) that occur in the spiritual areas , either in exploitation or abandoned deposits, this procedure is also applicable to industrial facilities that produce acid effluents. The process of the invention consists of three stages complementary to each other, such as: a) Selective removal of iron and acidity from the medium by biooxidation of Fe (II) and precipitation with alkalis (Ca (OH) ₂ , NaOH, KOH or NH ₄ OH) of the compounds of Fe (III). b) Taking advantage of the high sulphate content of mine acid waters for synthesis by ion exchange of K ₂ SO ₄ or (NH _J ^ SO _Í , free of chlorides that can be used as fertilizers or marketed in other applications. c) Recovery of the metals contained in these waters: Cu ²⁺ , Al ³⁺ , Zn ²⁺ and Mg ⁺ .

Each stage separately can lead to specific treatments of aqueous solutions, but only the proper combination of the three stages constitutes an integral solution to the problem posed by acidic waters. BACKGROUND OF THE INVENTION

Acid drains from metal sulfide mines constitute one of the most important ecological problems resulting from mining activity. Acid mine waters originate from oxidation of metal sulphides in contact with water and the atmosphere. Fe (II) is oxidized to Fe (III) by oxygen and by the action of bacteria such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans, subsequently hydrolysis of the formed Fe (III) takes place and the subsequent generation of acid. Acid mine waters are characterized by their low pH and high metal ion content and constitute a serious problem for nearby aquifers. The treatment of this type of water is necessary both from an ecological and economic point of view. The most frequently used methods for the treatment of industrial acid effluents with high metal ion content are a) Precipitation.

one Precipitation is one of the most frequently used methods in industrial acid water treatment processes. The most commonly used agents are alkalis (NaOH, CaCO ?, Ca (OH) ₂ , Na ₂ CO-, and mixtures thereof), sulphides and phosphates. The main disadvantages of this type of process are '- Incomplete precipitation (especially in the case of soluble hydro-complexes)

Toxicity of precipitating agents (case of sulphides and xanthates). Technical difficulties for mixing reagents with large volumes of effluent.

Technical difficulties in the filtration and decantation processes - Generation of huge amounts of toxic solid waste (metal pumps) that must be isolated in safety tanks at the risk of its concentrated dissolution, b) Solvent extraction

This technique is very suitable for the selective extraction of metals from aqueous solutions, however, in this case it has some drawbacks that make it inadvisable:

It is not a very suitable method for the treatment of large volumes of effluent and relatively low metal concentrations.

Losses of solvent and organic reagent are possible both by evaporation and by solubility in the aqueous phase, which given the enormous volumes that are treated, suppose a high economic cost and a potential risk of contamination for e! environment.

In some cases, interfaces are formed that prevent the rapid separation of the organic and aqueous phases c) Liquid membranes.

This new separation technique makes it possible to work at the high flows necessary for the treatment of this type of effluent and is suitable for the selective extraction of low metal concentrations. However, it presents some problems especially related to the stability of the liquid membranes that make this technique inadvisable.

SUBSTITUTE SHEET (REG.LA 26) EAPLICACTON OF THE INVENTION

The process for the treatment of acidic waters object of the present invention comprises three stages:

1) Stage of elimination of iron and acidity through biooxidation in which all Fe (II) is oxidized to Fe (HT), this process is carried out by percoiating the waters (6) through a biological reactor (1). This reactor contains an active population of ferrooxidant bacteria that are responsible for carrying out the biooxidation process.

Once all the Fe (13) has been oxidized, the compounds of Fe (III) are removed by precipitation (2) separating as sludge (8). This is achieved by raising the pH of the solution to values between 3 and 4, by adding either KOH, K ₂ CO ₃ , Ca (OH) ₂ , NaOH or NH 4 OH, (7) .

2) The second stage consists in taking advantage of the high sulphate content of these waters for the synthesis of K2SO4 or (H ∑SO- ,, chloride free by means of the ion exchange technique, products that can be used as fertilizers or marketed for other applications The process is carried out using a cationic exchanger in potassium or ammonium form (3) The passage of acidic water through the resin bed leads to the exchange of potassium or ammonium ions through the metal ions contained in the acidic water, obtaining a solution of K ₂ S0 or NH4SO4, pure respectively (lθ).

3) The last stage consists in the elution of the metal ions retained in the sulfonic resin with a concentrated solution (hereinafter, primary elution solution), either of KC1, of KjSO ₄ or of a mixture of both (in the if the sodium or ammonium form of the resin is used, the ammonium will substitute potassium in the chloride and sulfate salts used in the solution of pπmaria elution) (9) and the selective recovery of the metal ions of the acidic water using cationic exchangers weak (carboxylic resin) and chelating resins (4).

In this stage the regeneration of the sulfonic resin is carried out, the initial potassium or ammonium form being recovered and the resin being ready for the next stage after a water wash to remove the excess salts contained in the primary elution solution. The selective recovery of metals is carried out sequentially using columns connected in series with resins of suitable selectivity. At the exit of the column system a first fraction of Mg ^{~~ is obtained} (in the form of chloride, sulfate or the mixture of

3

SUBSTITUTE SHEET (RULE 26) both) (14) in KC1, K ₂ SO, medium, or the mixture of both (in the case of having used the ammonium form of the resin, the ammonium will replace potassium in the chloride and sulfate salts of the medium). Magnesium is recovered as Mg (OH) ₂ or passes to an additional ion exchange unit for separation along with the calcium remaining in the primary elution solution (5). On the other hand, the elution of resins with H SO ₄ (or HCl) (15) allows to obtain liquors of CuSO ₄ (1 1), Al ₂ (Sθ4) 3 (12) and ZnSO ₄ (13), which, in In the case of Cu and Zn and prior adequate conditioning can be subjected to electrolysis to produce electrolytic Cu and Zn. The Mg and Ca metals separated in the ion exchange unit are obtained as a mixture of the corresponding sulfates or chlorides after elution with the selected acid.

The spent primary elution solution, as a result of the metal recovery stage, has a high potassium (or ammonium) content and a small amount of metal ions such as Mn ⁺ that have not been absorbed by the resins. The elimination (17) of these metals (18) with suitable alkali (7) and the adjustment of both the pH with acid and the saline content (19), allows the reuse of this solution for the regeneration stage of the initial cationic resin ( primary elution solution).

BRIEF DESCRIPTION OF THE FIGURES

FIGURE 1: Flow chart of the procedure for the treatment of acidic waters. FIGURE 2: Scheme of the arrangement of ion exchange columns for the synthesis of K ₂ SO4 (or (NH ₄ ) ₂ S0 ₄ ) and the selective recovery of metals.

DETAILED DESCRIPTION AND MODE OF EMBODIMENT OF THE INVENTION

The study of the process of the invention has been carried out in the following stages: a) Characterization of acidic waters. b) Synthesis of K ₂ SO ₄ or (NH4) ₂ Sθ by the ion exchange technique. c) Study of the selectivity of different types of ion exchangers. d) Integral treatment of acidic waters. a) Characterization of Acid Waters Different samples of approximately 50 L volume have been studied. The corresponding analyzes have been carried out using the ICP technique (induction-collected plasma) for the determination of metals and total sulfate, and the potentiometric technique for

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SUBSTITUTE SHEET (REGl_A 26) the determination of the pH of the samples.

The Fe content of these samples is very high, between 4000 and 9000 ppm. The concentration of Zn ^{2 "} is also high. With cheers between 600 and 1500 ppm. The concentration of Cu ^{2 *} is about 10 times lower, between 60 and 250 ppm. Other metals whose concentration is relatively high are: Al ^5" (450 -650 ppm), M ² (800-900 ppm), Ca ^{2 *} (350-500 ppm) and Mn ^{2 "} (70-100 ppm). The sulfate content varies according to the samples between 18 and 32 g / L. The pH varies between 1.8 and 2.2 The content of other metals as well as chlorides is practically negligible, b) Synthesis of K ₂ SO ₄ or (NEL ^ SO. ,, Through the Ionic Exchange Technique It has been used the high sulfate concentration of acidic waters to synthesize

K ₂ SO ₄ or (NϊL,) ₂ SO ₄ free of chlorides that can be used as fertilizer before or marketed for other applications.

In this study the commercial resin Lewatit SP 1 12 (Bayer) has been used. This resin is a strong cationic gel-type exchanger with cross-linked polystyrene with divinylbenzene being the sulfonic acid functional group. This resin has been conditioned in potassium (or ammoniacal) form, using the corresponding primary elution solution (see the Explanation of the Invention section).

The passage of the acidic water through the resin bed charged in potassium (or ammonium) form allows to obtain a solution of K ₂ SO ₄ ((NH) ₂ SO ₄ ), completely free of the metal ions of the initial solution. From this solution it is possible to obtain the corresponding salt by christization or by reverse osmosis.

The regeneration of the sulfonic resin is carried out with the primary elution solution which, as already described, is a concentrated solution of either KC1, either K ₂ SO ₄ or one of its mixtures (in the case of using the resin in ammonium form, the ammonium will replace potassium in the primary elution solution), which causes the elution of the metal ions retained in the resin. In this way, a concentrated solution of the different metal ions (between 4 and 8 times) is obtained and the initial potassium (or ammonium) form of the resin is recovered at the same time, remaining ready for the next stage after washing with water . The wash water is recirculated and used for the preparation of the primary elution solution.

SUBSTITUTE SHEET (RULE 26) c) Selectivity of the Different Ionic Exchangers

The recovery of the different metal ions of the acidic water is carried out using ion exchangers of appropriate selectivity for each case.

A study of the selectivity and capacity of weak cation exchangers and chelators has been carried out. Studies have been carried out using a resin with a carboxylic functional group (Lewatit R 250-K or CNP 80) and another with iminodiacetic acid (Lewatit TP-207 ) from the Bayer house.

The carboxylic resin has been highly selective to Al ^{', +} , being very suitable for the recovery of this metal. This selectivity increases dramatically with the increase in temperature of the loading solution, which is a way to achieve greater purity of the recovered aluminum. On the other hand, the resin with iminodiacetic acid has been very selective for Cu ^{2 *} . This resin also allows the recovery of Zn ²⁺ in the event that Cu ²⁺ and AT ^* are previously removed from the solution, since these two metals are preferentially absorbed. d) Integral Treatment of Acid Waters

The first stage consists of a pretreatment of acidic waters. This process consists of the biooxidation of Fe (II) by bacteria of the Thiobacillus Ferrooxidans type and subsequent precipitation of Fe (III) compounds by measuring the addition of alkali to a pH between 3 and 4 and adding a suitable flocculant for rapid total precipitation. The next stage consists in the recovery of the different metals eluted from the sulfonic resin in the regeneration stage of said resin. Recovery takes place sequentially using a system of fixed bed columns connected in series (see Fig 2). Each column is tripled (two connected and one in regeneration), so that the process can be developed continuously and the treatment of the solution can be continued while elution and regeneration of the spent resin occurs.

Columns 1 and 2 are filter beds to remove suspended fines. The synthesis of K ₂ SO ₄ (or (NH4) ₂ SO ₄ ) is carried out in columns 3 and 4 (Lewatit SP1 12) during the charging process with acidic waters. The solution resulting from this process containing virtually pure K SO ₄ or (NH4) SO ₄ is treated in a reverse osmosis unit to achieve product concentration and a considerable volume of water suitable for irrigation. The separation and recovery of Cιr ^~ is carried out in columns 5 and 6 (Lewatit TP-207), from the solution obtained during the regeneration process of the resin contained in

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SUBSTITUTE SHEET (RULE 26) columns 3 and 4 with the primary elution solution The separation and recovery of Al ^"" is carried out in columns 7 and 8 (Lewatit CNP 80) and that of Zn ^{2 "} in columns 9 and 10 (Lewatit TP-207) The successive elimination of Cu ^{2 "} , AT ^" and Zn ²⁺ allows the partial recovery of Mg ²⁺ at the exit of the column system, or its separation (together with the remaining calcium) by an additional ion exchange unit (carboxylic resin, Lewatit CNP80) which is in the appropriate cathonic form (potassium or ammonium) to contribute to the regeneration of the primary elution solution (eluent of the first ion exchange unit columns 2 and 3).

The removal of residual metal ions in the primary elution solution, after selective recovery of Cu ²⁺ , Al ³⁺ , Zn ²⁺ and Mg ²⁺ is carried out by precipitation by adjusting the pH between 10 and 12 with alkali appropriate. The precipitate of metal hydroxides removed from the primary elution solution (practically Mn ²⁺ ) is separated for later recovery or sent to the process head (acid water inlet)

SUBSTITUTE SHEET (REG.LA 26)

Claims

1 Procedure for the treatment and decontamination of acidic waters containing dissolved metals and their conversion into fertilizers, said metals being mainly: ferrous iron, ferric iron, copper, zinc, aluminum, magnesium, calcium and manganese at a pH below 3.5 . The process consists of the following stages: a) Biooxidation of Fe (II) to Fe (III) by causing the water to percoiar through a reactor that supports an active population of ferrooxidant bacteria. b) Removal of iron by precipitation of Fe (III) hydroxides by raising the pH so that most of the other metals are kept in solution. c) Synthesis of potassium sulfate or chloride-free ammonium sulfate, from acidic waters using a non-selective ion exchanger that will be in potassium or ammonium form. d) Recovery of metals contained in acidic waters, eluted during the regeneration stage of the previous resin by means of a regenerating solution based on

KCI, K ₂ SO ₄ or a mixture of both salts, applying a process of selective separation of metal ions using carboxylic resins and chelators. e) Elimination of residual metric ions in the regeneration solution used in the previous stage, adjustment of pH and saline content, so that said solution can be reused.

2. Method according to claim 1 characterized in that the biooxidation of Fe (II) is carried out by biological catalysis with ferrooxidant bacteria from habitats directly related to the acidic waters to be treated.

3. Method according to claims 1 and 2 characterized in that the biooxidation of Fe (II) is carried out in fixed or fluidized bed bioreactors and with the populations of bacteria fixed in inert supports.

4. Method according to claims 1 and 3 characterized in that the aicalinization of the acidic waters is carried out with Ca (OH) ₂ , KOH, K ₂ CO ₃ , NH OH or a mixture of these compounds.

5. Method according to claims 1 to 4, characterized in that the synthesis of potassium sulphate or chloride-free ammonium sulfate is carried out from the solution obtained from the acidic waters, once the iron is removed, by means of a canonical resin.

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SUBSTITUTE SHEET (RULE, 26)

Method according to claims 1 to 5, characterized in that the regeneration solution of the non-selective cationic resin is based on ammonium chloride, ammonium sulfate or a mixture of both salts, instead of potassium salts.

Method according to claims 1 to 6, characterized in that the recovery of Cu ²⁺ , Al ^τ , Zn ⁺ and Mg ⁺ from the regeneration solution of the previous resin is done sequentially using different types of resins with the appropriate selectivity for each metal.

Method according to claims 1 to 7, characterized in that the separation of Mg " ⁺ from the regenerating solution is carried out jointly with Ca ²⁺ using an ion exchange unit connected in series to the sequence of resins that selectively separate Cu ⁺ , Al ^3" and Zn ²⁺ .

9. Method according to claims 1 to 8 characterized by the performance of the ion exchange process at temperatures above 20 C

10. Method according to claims 1 to 9 characterized by the use of both fixed bed and fluidized bed columns in ion exchange processes.

11. Method according to claims 1 to 10 characterized by the use of a reverse osmosis membrane unit for obtaining potassium sulphate or concentrated ammonium sulfate and water with suitable characteristics for irrigation.

12. Method according to claims 1 to 11 characterized by the use of electrolysis units for obtaining metallic Cu and Zn.

13. Method according to claims 1 to 12 characterized in that said waters come from active or inactive mining facilities, industrial facilities with natural or artificial production of acid effluents or river basins, streams, lagoons, etc. which due to their contact with masses of minerals are contaminated by acid and heavy metals.

SUBSTITUTE SHEET (RULE 26)