NL1004324C2 - Treatment of metal-containing waste and/or organic waste - Google Patents

Abstract

The comprises reacting both types of waste together in the presence of water and separating the resulting mixture into a mainly liquid component and a mainly solid component.

Description

Method for treating metal-containing waste and / or organic waste.

The invention relates to a method for treating metal-containing waste and / or organic waste, wherein in particular both types of waste can be processed simultaneously.

Such a method is known from German patent application 4,321,089, wherein water or sludge contaminated with heavy metals is treated in the presence of water with a vital or devitalized biomass obtained from water algae living on the seabed, whereby the heavy metals are absorbed by absorption. absorbed by the biomass, the heavy metal-contaminated biomass is separated from the purified water or the purified sludge and the contaminated biomass is dried and discarded as waste. A drawback of this method is that a very specific biomass has to be used and that a waste product is formed which is highly contaminated with heavy metals.

In many metal extraction and metal processing processes, a large amount of non-further processable metal-containing waste is released. The main metal component is often divalent or trivalent iron, which in itself does not present major problems, but the large volume in which this iron is contained, as well as the accompanying very objectionable other heavy metals, such as copper, germanium, cadmium, antimony, mercury, lead and others , make discharge difficult, if not unacceptable and reprocessing is very expensive.

This is how zinc production by the so-called jarosite process produces large quantities (about 0.6 tons dry weight per ton zinc produced) ammonium jarosite, a water-insoluble iron (III) -containing salt with the gross formula MFe3 (S0i,) 2 (0H ) 6 (M = NH * ,, 30 Na, K, Ag and / or i Pb) as residual product. The product, a yellowish paste, contains besides jarosite itself a few percent lead and zinc and noticeable amounts of other metals such as copper, nickel and cadmium, and metalloids, such as arsenic. The jarosite waste is acidic, with a pH of 2, and contains large amounts of heavy metals. The jarosite process 35 produces approximately JQ% of world zinc production. Other processes for the production of zinc, such as the hematite process and the goethite process, also produce ferrous waste (mainly Fe2O3 and FeOOH, respectively), which also contains heavy metals.

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Another type of metal-containing waste to consider is the metal-containing sludge that arises in large quantities during the processing from bauxite to aluminum. A waste that could also be treated are the residues from the reprocessing of manganese ores.

5 This waste mainly consists of iron (III) and manganese (IV) oxides.

The average composition of jarosite waste is shown in Table A:

Table A: Jarosite composition in g / kg: 10 Aluminum (oxide) 10 Magnesium (oxide) 2.2

Ammonia 17 Manganese 0.8

Antimony 0.3 Nickel 0.01

Arsenic 2 Silicon (oxide) 50

Cadmium 0.4 Hydrogen 9 15 Calcium (oxide) 30 Iron 250

Chrome 0.3 Silver 0.2

Cobalt 0.1 Zinc 25

Copper 0.7 Oxygen 390

Mercury 0.05 Sulfur l40 20 Lead 50 other 23

In order to reprocess jarosite-containing waste, international patent applications WO-A-88039H and WO-A-8803912 propose treating the waste with calcium chloride and sulfuric acid, respectively, whereby part of the metals present can be recovered. According to European patent application 31667, lime cement and an aluminum and silicon-containing powder are added to ammoniumjarosite, after which a product is obtained which can be dumped. However, such and other methods are not satisfactory and / or expensive.

Another method for the reprocessing of jarosite waste is the so-called oxysmelt process. Jarosite is dried and melted with oxygen at about 2000 ° C, whereby after further treatments an iron-containing slag, a lead and / or silver-containing fraction, recoverable zinc and sulfuric acid are formed separately. However, this process is energy intensive and further requires facilities such as flue gas desulfurization installations and fly ash traps that make the process extra expensive.

As a result of the drawbacks of such processes, jaro-40 site waste has hitherto not been processed, but landfilled or discharged into sea or other water. Therefore, there is a great need for cost effective methods for the reprocessing of waste waste containing jarosite 1004324 3 and other metal-containing waste.

Organic waste of various kinds is widely produced in large quantities. It is usually processed by incineration, biological treatment or landfill. Special types of organic waste are 5 sewage sludge and the waste that comes from the factory industry, and in particular the liquid or semi-liquid manure-containing waste (floating manure). Although animal manure waste can in principle be used for fertilizing agricultural land, the locally produced very large quantities and the unbalanced composition thereof, such as a high ammonia content and the presence of heavy metals, cause a sometimes unacceptably high burden on the environment when applied. on (eutrophication and acidification). Table B lists, for example, the contents of elements other than carbon, nitrogen and hydrogen in pig manure (in g / kg).

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Table B: Pig manure composition in g / kg

Sodium 12 Manganese 0.4 Phosphorus 20

Potassium 100 Copper 0.6 Nitrogen 117 20 Calcium 23 Chromium 0.02 Chlorine 2.7

Magnesium 12 Zinc 0.7 Sulfur 4.4 Iron 3.5 Nickel 0.03 25 Moreover, with such organic waste there is a significant odor problem. Sewage sludge, originating from wastewater treatment plants, is also a type of waste whose processing causes problems because of the quantities and the composition. Various methods have been proposed for the processing of such organic waste, but as far as they are economically feasible, the capacity is insufficient and a transport problem is often encountered. There is therefore a need for additional methods for inexpensive processing of organic waste, such as animal manure.

It has now been found that metal-containing waste and / or organic waste can be processed in a particularly advantageous manner by allowing both types of waste to react with each other, preferably at a temperature above 100 ° C, in the presence of water and separating the resulting mixture in a substantially liquid component and a substantially solid component.

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The method according to the invention therefore has the great advantage that two problems, namely that of the processing of metal-containing waste and that of organic waste, are eliminated at the same time.

An advantage of the method according to the invention is that the amount of solid residue decreases sharply when processing metal-containing waste, in particular iron (III) -containing waste. The heavy metals are wholly or almost entirely stored in the solid phase, while sulfur in the form of substantially sulfate is almost entirely dissolved in the liquid phase. This separation of metals and sulfur can be optimized by controlling the pH. The pH is adjusted to a value between 4 and 11, preferably between 5 and 9 and in particular between 6 and 8. Adjustment of the pH to the desired value can be accomplished by adding a base such as magnesium 15 oxide and ammonium hydroxide. A further advantage of a correct adjustment of the pH is an increase in the reaction speed, because the reduction of jarosite mainly takes place according to the half reaction: MFe3 (SOi |) 2 (OH) 6 + e + 2 OH '-> M * + Fe30 + 2 SO2; + 4 H20 20

The organic waste used in the method according to the invention preferably contains oxidizing agents, that is to say means which can effect the above half reaction by electron transfer. An example of a suitable oxidizer is cellulose.

The solid residue is a fine-grained crystalline substance, which, depending on the type of metal-containing waste, mainly consists of, for example, hematite (Fe2O3), magnetite (Fe30i) or anglesite (PbSOJ. Preferably, the method according to the invention is carried out in such a manner. that from the jarosite mainly magnetite and galena (PbS) and to a lesser extent hematite and anglesite are formed.

By means of mineral separation and / or hydrometallurgical / pyrometallurgical operations, fractions with a high content of heavy metals, in particular lead and silver, can then be obtained from the solid residue (the reacted mixture). The metals can be recovered from these concentrates, so that the residual iron-rich residue is less toxic and occupies a smaller volume.

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Especially when using an excess of organic waste, melting is preferred as a pyrometallurgical method for the treatment of the solid residue. Namely, it has been found that the organic matter is decomposed in such a way that the solid residue obtains a certain energy value, for instance due to the presence of carbon, whereby the energy balance of a thermal post-treatment of the solid residue is improved.

Another advantage of the method according to the invention is that the organic waste is decomposed quickly and efficiently and is (partially) oxidized without the need to compress large amounts of air. Heavy metals present in the organic waste are also largely stored in the solid fraction and other nuisance components, such as nitrogen and sulfur compounds, are made less harmful in the process: sulfur compounds are oxidized to sulfate and nitrogen compounds are converted into ammonium. This leaves a liquid component that can be discharged without objection, possibly after a further (simple biological) treatment.

The method can be described as a wet oxidation of the organic waste with a simultaneous wet reduction of metal-containing waste. In principle, the process can be carried out at the prevailing outside temperature if a low reaction speed is not a limitation, for example in the in situ treatment of metal-containing waste. However, a reasonable reaction speed of this process requires a temperature above 100 ° C, so that the process is preferably carried out in a closed system. If the process is carried out on the earth's surface, it is necessary to keep the system under pressure. Industrial autoclaves known per se can be used for this.

A possible embodiment of the method according to the invention consists in reacting the organic waste and the metal-containing waste in an underground reaction vessel at an elevated temperature.

The surrounding earth layers have very good thermal insulation, so that the energy efficiency of the process is optimal. The main role of this embodiment, however, is that the column of the reaction mixture present above the reaction zone provides the necessary pressure, so that this mixture does not boil even at a reaction temperature of 200-300 ° C; it is therefore referred to as "wet" oxidation. A temperature of 200-300 ° C has proved particularly advantageous for the present process.

The process can be carried out as a continuous process, with the reaction mixture being introduced at the surface of the earth. The reaction mixture is then introduced into the reaction vessel under such pressure (minimum 10 bar, maximum 90 bar, especially 30-55 bar) that both friction losses are compensated and the outlet pressure can be kept at about 8 bar. After reaction, the reaction products are returned to the earth's surface. Advantages of such an embodiment are, in addition to the continuous implementation, the avoidance of compression work for the reaction at high temperature, an inherent reactor safety, a small space requirement above ground and a good thermal insulation of the reaction zone by the surrounding rock formations.

Such a reaction vessel is known per se from European patents 18,366, 281,302 and 282,276. In the known installations, however, oxygen is introduced for the oxidation of sewage sludge, which oxygen injection is not required in the present process.

Any waste containing reducible metals, in particular iron (III), can be considered as metallic waste. The present method is advantageous especially for metallic waste containing other heavy metals, because such waste is otherwise difficult to process. Particularly suitable for treatment by the present process is the ferrous waste from zinc fabrication, which has jarosite as the main component.

Any type of semi-solid or liquid organic waste can be considered as organic waste in the present process. Preferred are manure-containing waste such as slurry. This may concern waste containing manure from cattle, pig and poultry fattening farms. Pig manure is particularly suitable due to its nature and quantities. Another preferred type of organic waste is sewage sludge, which is also available in large quantities.

35 The mutual ratio of the amounts of the two types of waste to be used depends on the type of waste to be processed primarily, the dilution degree of the waste, its acidity and other properties. Generally, an excess of 1004324 7 of the organic waste, especially when it is liquid manure-containing waste, will be used. A useful excess of pig manure, for example, is an amount of 6 or more parts of pig manure on 1 part of jarosite waste.

The process according to the invention can for instance be carried out in an installation as shown in figure 1. The two types of waste are led one after the other or after mixing via a pipe 1 into a subterranean reactor 2 where the mixture is brought to temperature , for example 250-300 ° C, by means of a heating device 3. When the mixture has the desired temperature, further heating is no longer necessary, because the reaction proceeds exothermically. After a residence time of about 1 hour, the mixture returns from the reactor via a second tube 4, which is connected to tube 1 by means of heat exchangers 5. The effluent reaction product is collected in a basin 6, where the solid phase settles. The above solution is pumped into a facility for (biological) post-cleaning and then discharged. If necessary, the solid phase is separated into a magnetite-containing fraction and a non-magnetic fraction, which can serve as secondary lead and zinc ore. It may be desirable to produce from the solid phase hydro- or pyrometallurgical concentrates of lead, silver and zinc from which these metals can be recovered.

Table C shows, for example, the composition of a solid fraction obtained after treatment of jarosite waste with pig manure. The second column lists the contents in a sample in which the supernatant had a final pH of 4.7 by adding about 1% by weight calcium hydroxide; Anhydrite (CaSO /,) was formed and zinc and cadmium also precipitated, in addition to an additional amount of iron. The last column refers to a sample whose final pH in the liquid was 1.8, with some of the zinc and iron remaining in the solution.

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Table C

element content (g / kg) content (g / kg) pH = 4.7 pH = 1.8 5 -

Ag 0.25 0.26

Al 4.5 3.8

Cd 0.67 0.49

Cu 2.2 2.2 10 Fe 228 190

Mg 4.3 4.5

Ca 56 (1) 11.7 p 8.1 3.5

Pb 67 71 15 S 71 35

Zn 39 16 (1) after addition of calcium hydroxide. In Table D the contents of the jarosite waste to be treated, in the solid residue obtained and in the liquid formed therein are shown for a number of elements. It has been found that the concentration of the various elements in the residual liquid has fallen to an acceptable value.

Addition of, for example, about 8% by weight of MgO to the reaction mixture raises the final pH of the remaining liquid to about

7.5 and brings the concentration below the detection limit for all heavy metals. The result is an effective separation of sulfur and heavy metals. About 90-95% by weight of the sulfur goes into solution 30, while the sulfur content of the solid residue is generally less than 2% by weight. The latter is of great importance since a sulfuric acid plant is no longer required for the thermal treatment of the residue.

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Table D

element content (g / kg) content (g / kg) content (g / 1) in jarosite in solid residue in liquid 5 -

Ag 0.17 0.20 n.d.

Axis 2.1 4.1 0.017

Cu 0.69 2.3 n.d.

Pb 48.5 73.9 n.d.

10 Zn 21.1 24.9 0.15 n.d .: not detectable

The liquid component can for instance be further treated by, for example, removing sulphate and ammonium ions from it or converting it into harmless products. Such treatment can be, for example, treatment with a base to form gypsum or with bacteria capable of converting sulfate to sulfur. The use of bacteria that convert sulfate to sulfur can be particularly advantageous, because this creates base which can be recycled back into the process for treating the metal-containing waste. For example, one can remove ammonium ions by, for example, treating the liquid component with bacteria that can convert ammonium ions into nitrogen. It will be clear that the order of these treatment steps strongly depends on the relative amounts of substances to be removed or converted, such as sulphate and ammonium ions. It is also possible that only the sulphate is removed from the liquid component, after which the purified liquid component is used as fertilizer, optionally after addition of additional carbon source.

The invention will be further illustrated by the following examples.

Example 1

A Parr Mini Reactor model 4563 autoclave with a volume of 600 ml was used, the autoclave being equipped with a double six-bladed turbine stirrer (diameter 5 cm), which was connected by magnetic coupling to a stirring motor, and was equipped of a 500 ml glass vessel, which was filled with liquid in the experiments to a volume of approximately 10%. The autoclave was also equipped with a tube that reached into the liquid and a sample chamber, so that samples could be taken during the tests. The autoclave was also equipped with taps so that it could be purged with nitrogen. The tests were started at a pressure of 5 bar. The time taken to bring the contents of the autoclave to the desired temperature depended on the height of this desired temperature: 20 minutes before reaching 175 ° C and 48 minutes before reaching 300 ° C. After the reaction, the autoclave was cooled in water. The tests were carried out with a suspension of 125 g of jarosite in 500 ml of sewage sludge containing 5% by weight of sludge, the suspension thus obtained being made up with water to a volume of 1 liter. The solids content was 15% by weight. The compositions of the jarosite and sewage sludge are summarized in Table E.

Table E

Element (wt%) Jarosite Sewage sludge c 27.8 N 0.9 5.9

After 1.3 0.5 20 Mg 0.0 0.8

Si 2.7 4.9 P 3.1 S 11.2 0.8

Ca 0.3 2.6 25 Fe 26.7 1.3

Zn 2.7 0.1

Pb 3.5

Aga 80

Cda 79 30 Dry weight 60 95 a ppm.

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The tests were carried out for 1 hour at a temperature of 280 ° C and a pressure of 65 bar.

Figure 2 shows the decrease of the iron concentration in the liquid component as a function of the pH (adjusted by adding magnesium oxide). At a pH of about 7, essentially all of the iron is present in the solid component.

Example 2

The experiments of Example 1 were repeated, except that ammonium hydroxide was used as the base.

Figure 3 shows the decrease of the iron concentration in the liquid component as a function of the pH (adjusted by adding magnesium oxide). At a pH of about 7, essentially all of the iron is present in the solid component.

Example 8 A test according to the procedure of Example 1 was carried out at a pH of 6.5. The minerals formed were found to be mainly magnetite, franklinite (ZnFe30 /,) and magnesio ferrite. The particle size was about 1 - 5 µl. The resulting gas mixture was found to contain more than 95% carbon dioxide. Table F shows the mass bales of the test.

Table F

Incoming flows Outgoing flows

Element Liquid Solid Liquid Solid component component component component (wt%) (wt%) (wt%) (wt%) S (total) 2 98 86 14 25 Fe 0 100 1 99

Zn 0 100 0 100

Pb 0 100 0 100

Mg 100 0 89 11 NHJ 56 44 86 14 30 Ca 35 65 26 74 1004324

Claims (11)

1. Method for treating metal-containing waste and / or organic waste, characterized in that the two types of waste are reacted with each other in the presence of water and the resulting mixture is separated into a mainly liquid component and a mainly solid component. A method according to claim 1, wherein both types of waste are reacted with each other at a temperature above 100 ° C. 10 A method according to claim 1 or 2, wherein the acidity during the reaction is kept between the values pH = 4 and pH = 11. A method according to any one of claims 1 to 3, wherein the metal contains waste iron and optionally other heavy metals in an oxidized state. 15 Method according to any one of claims 1-4, wherein the metal-containing waste contains jarosite. A method according to any one of claims 1-4, wherein the metallic waste contains residues from the bauxite processing. A method according to any one of claims 1-4, wherein the metal-containing waste is residues from the processing of manganese ores. A method according to any one of claims 1-7. the organic waste containing manure, in particular pig manure, or sewage sludge. 9. A method according to any one of claims 1-8, wherein the waste is reacted in an autoclave at a temperature of 200-300 ° C. The method of claim 9. wherein the waste is allowed to react for 0.2-10 hours. 11. A method according to any one of claims 1-10, wherein the waste is reacted in an underground reactor. **** 1004324