MXPA99002835A - Process for the conversion of iron bearing residues into a synthetic rock - Google Patents

Abstract

This invention relates to the conversion of iron bearing residues from the non-ferrous process industry into a synthetic rock, comprising the following steps:1 part of the wet residue is mixed with at least 0.1 parts by weight of crushed blast furnace slags and with at least 0.1 parts by weight of crushed converter slags;water is added to the mixture to obtain a stiff paste;and the paste is allowed to harden, while kept wet, to such an extent that the resulting rock is usable for construction purposes.

Description

PROCESS FOR THE CONVERSION OF RESIDUES THAT CONTAIN IRON TO A SYNTHETIC ROCK DESCRIPTION OF THE INVENTION This invention relates to a process for the conversion of iron-containing waste from the non-ferrous process industry to a synthetic stone. Iron-containing waste is a typical by-product of the non-ferrous industry, particularly the zinc processing industry. Indeed, a well-known technique of zinc production involves the electrolysis of a solution of zinc sulfate. One of the main impurities that has to be removed from the solution before electrolysis is iron. For this purpose, the iron is precipitated and separated from the zinc solution, forming a residue containing iron. This residue contains most of the iron initially present in the solution, a significant amount of lead, arsenic, silica and residual zinc. Depending on the conditions that prevail before and during the separation, the iron in the residue is obtained as jarosite, goethite, hematite or magnetite. In particular, jarosite and goethite have no commercial value and are considered hazardous waste. Waste disposal sites have to be severely controlled and protected against impregnation by leaching. The stabilization and solidification of hazardous industrial waste is a global environmental technique, generally described in "Stabilizing hazardous aste", J.R. Conner, Chemtech, December 1993, pp. 35-44. Most solidification and inorganic stabilization techniques use pozzolanic reactions, that is, reactions of the type that occur in Portland cement, forming complex hydrated systems between CaO, A1203, S? 02 lMgO and Fe203. A known application of this technique in the zinc industry is described in EP-A-0031667. This document deals specifically with the treatment of arosite, and proposes a method to solidify it by mixing it with calcium containing a cement powder and a powder based on alumina and silica (inclusions in metals). The product has a claimed compressive strength of 0.64 MNm-2 after 28 days of hardening and exhibits low 11 x i vi to 11 day d.

However, this treatment process for jarosite has certain disadvantages: the product obtained has a relatively low compressive force making the product suitable for packaging, but unsuitable for the construction industry; the important case of lead lixivity is not mentioned; and a substantial amount of Portland cement is added which degrades the economics of the process. The purpose of the present invention is to bring a process with the conversion of waste containing iron from the non-ferrous industry to a synthetic rock, which avoids the disadvantages of the process described in EP-A-0031667. Up to this point, according to the invention: 1 part of the wet waste is mixed with at least 0.1 parts by weight of blast furnace slag crushed and with at least 0.1 part by weight slag from the crushed converter; Water is added to the mixture to obtain a consistent paste; and the paste is allowed to harden, while remaining moist, to such an extent that the resulting rock is usable for the purposes of construction. It has been found, in fact, that blast furnace slag and converter slag, which are by-products of the steel and iron manufacturing industry, act as particularly effective reagents of pozolan cuanao mixed with iron-containing waste : after hardening, a product is obtained with extreme hardness, comparable to the hardness of the concrete; this product exhibits on the other hand a very low lixiability; low porosity and good resistance to freezing, which is suitable for construction purposes. It is worth mentioning that blast furnace slag and steel and iron industry converters are very cheap reagents. In fact, the slag of the converter is waste without market value: having found an application for these slags, there is an additional benefit for the environment.

Of particular interest is the low leaching of lead that would otherwise have a dangerous environmental impact and prohibit the use of the product as a construction material. It is believed that the insolubility of lead is due to the presence of sulfides in blast furnace slag. The process claimed in this way not only results in the elimination of the waste, but also makes a chemical bond between at least some components. It should be mentioned here that in JP-02-233539-A blast furnace slag is mixed with steelmaking slag to form a slag block with the addition of Portland cement. Also in JP - 52 - 058728 - A a mortar is obtained by mixing blast furnace slag or converter with the blast furnace slurry and an alkaline stimulant and (b) an industrial waste slurry. In the DE-A-3915373 on the other hand the slag of the converter is mixed with the waste of a thermoelectric or steel plant to obtain material for the construction of roads. In G B - A - 2137186, the road construction material is obtained by mixing pozolana or blast furnace slag, together with steel production slag and a filling material. The residue, for example, goethite, is supposed to be thoroughly washed, this stage being an integral part of the elaboration diagram for the zinc process. The purpose of this washing step is to recover the residual soluble zinc and recycle it directly in the zinc plant. The slags are advantageously crushed to a particle size of less than 500 μm; less than 250 μm is preferred and less than 125 μm is even more preferred. Larger particle sizes are less reactive, but nonetheless allow coexistence with finer sizes as they are mechanically measured in the product. Slag from blast furnaces generally has a relatively low free content of CaO due to the content of high A1203 and high S2 02, which are well known to bind CaO. The typical concentration ranges in blast furnace slag are (by weight%): 25 to 45 of S i O; 6 to 20 of A 12 O 3; 0 to 5 of Faith; 0 to 10 MnO; 30 to 50 CaO; 2 to 11 MgO; and 0.1 to 5 sulfur.

Slag in the converter generally has a relatively high free content of CaO due to the low contents of A120, and Si02. The typical concentration ranges in the slag of the converter are (% by weight): 5 to 25 of S? 02; 0 to 5 of A1203; 5 to 25 of Faith; 2 to 15 MnO; 30 to 60 CaO; and 0 to 5 MgO. The amount of blast furnace slag and converter slag is preferably at least 0.4 parts per part wet residue. Very good results have been obtained when at least 0.2 parts of slag from blast furnaces and at least 0.2 parts of converter slag are used per part of wet residue. The best results obtained, however, were using at least 0.4 parts of slag from blast furnaces and at least 0.4 part of converter slag by number residue. It is not advisable to use more than 2 parts of each of both slags by the wet waste, because this would unduly increase the investment costs for the equipment required to carry out the processes of the invention. It is even more preferred to use no more than 1 part of each of the two slags per wet waste part, and even more preferred to use no more than 0.8 part of each of the two slags per part of the wet waste. In order to shorten the hardening time, it may be useful to add up to 0.1 part of cement, especially Portland cement, either to the mixture, or to the paste. The synthetic rock obtained by the process of the invention can be used as such, for example, in captive construction. It can also be crushed to produce gravel, which can be used in road construction, or for the production of concrete for the construction industry. In a special embodiment of the process of the invention, the paste is allowed to harden partially, broken to a suitable size, for example, gravel size, and then allowed to harden completely. The hardening is preferably carried out while the paste is submerged under water. The present invention is also related to the construction material containing the synthetic rock produced by the process of the invention. The invention will now be illustrated with the following examples. Slag from blast furnaces in the examples are classic slag produced by the steel and iron industry. The converter slags used are produced by the Linz and Donawitz (LD) conversion process. Through these examples, the slags are used according to the analyzes given in Table 1 and used with the analyzes given according to the goethite in Table 2. The goethite has 45% moisture by weight.

Table 1: Slag analysis Table 2: Analysis of Goetite T h e 1 For 1 part of wet goethite, 1 part by weight of blast furnace slag, and 0.5 part of slag from the converter are added. The slags are crushed at 150 μm or less. The ingredients are mixed and the necessary amount of water is added to obtain a hard paste. This paste is hardened for 2 months under water. The product obtained is both very hard and inert. The results of the hardness and lixivity tests are summarized in Table 3 below.

E j p lo 2 For one part of the wet goethite, 0.5 parts by weight of slag from blast furnaces, and 0.75 parts of slag from the converter are added. The slags are crushed at 150 μm or less. The ingredients are mixed and the necessary amount of water is added to obtain a consistent paste. This paste is hardened for 2 months under water. The product obtained is both inert and very hard. The results of the hardness and lixiability tests are obtained in Table 3 below.

E j em lo 3 For 1 part of wet goethite, only 0. 1 parts by weight of slag from blast furnaces, and 0.5 part of slag from converter are added. The slags are crushed at 150 μm or less. The ingredients are mixed and the necessary amount of water is added to obtain a consistent paste. This paste is hardened for 2 months under water. The product obtained is relatively hard and totally inert. The relative hardness makes this product still suitable for construction purposes, for example, for the construction of roads. The results of the hardness and lixiability tests are summarized in the Table 3 below. Table 3: Results of examples 1 to 3 The hardness reported in the previous table is the hardness constrained. The lixiability reported in the table above is' measured in accordance with the DIN S 4 standard.

Claims (12)

1. A process for the conversion of iron-containing waste from the non-ferrous processing industry to a synthetic rock, characterized in that: 1 part of the wet waste is mixed with at least 0.1 parts by weight of blast furnace slag crushed and with minus 0.1 parts by weight of crushed converter slag; the water is added to the mixture to obtain a consistent paste; and the hardening of the paste is allowed, while it remains humid, to such an extent that the resulting rock can be used for construction purposes.

2. The process according to claim 1, characterized in that the iron-containing residue is goethite.

3. The process according to claims 1 or 2, characterized in that for 1 part of wet waste, a total slag amount of at least 0.4 parts is used.

4. The process according to any of claims 1 to 3, characterized in that for 1 part of wet residue, at least 0.2 parts, preferably at least 0.4 parts, of each of both slags is used.

5. The process according to any of claims 1 to 4, characterized in that for 1 part of wet residue, no more than 2 parts, preferably no more than 1 part, of both of the slags is used.

6. The process according to any of claims 1 to 5, characterized in that a part of the wet residue, not more than 0.8 parts of each of both slags is used.

7. The process according to any of claims 1 to 6, characterized in that the slags are crushed to a particle size of less than 500 am, preferably less than 250 pm, and more preferably less than 125 pm.

8. The process according to any of the rei indications 1 to 7, characterized in that for 1 part of wet waste, up to 0.1 part of cement is added, either to the mixture, or to the plant.

9. The process according to any of claims 1 to 8, characterized in that the synthetic rock is ground to produce gravel.

10. The process according to any of claims 1 to 8, characterized in that the pulp is first allowed to harden partially, and then ground to a suitable size, and then allowed to harden completely.

11. The process according to any of claims 1 to 10, characterized in that the paste is allowed to harden while being submerged under water.

12. A construction material containing the synthetic rock obtained by the process according to any of the rei indications 1 to 11.