CS228201B1 - Method for removal chromium from iron ores with low nickel and chromium content - Google Patents

Description

SUMMARY OF THE INVENTION The present invention provides a process for the removal of astonishment from a low nickel and chromium iron ore or from a chromium-containing iron ore or a ferrous-iron slag by pressure alkali-oxidative leaching, which is particularly suitable for complex processing of laterite Fe-Ni-Cr ores; raw materials for nickel and cobalt, compounds or alloy alloys or chromium metal and pig iron or steel.

Laterite Fe-Ni-Cr ores are currently used mainly for the production of nickel and cobalt essentially by various variations of the Caronova method. Representative of this type of ores is the Albanian Fe-Ni-Cr ore (see Table 1). The ore is then crushed, judged, finely ground (90% below 0.1 mm), roasted at a temperature of about 700 ° C and finally leached with an ammonium ammonium carbonate solution.

Table 1 Albanian Fe-Ni-Cr ore component Ni-leach mass % wt. %

Fe cel. 49.0 to 51.0 55.0 to. 58.0 Ni 0.95 to 1.05 0.28 to 0.30 Cr 2.2 to 3.0 2.32 to 2.78 What 0.05 0.02 to 0.03 AI2O3 4,5 to 6.5 5.0 to 6.0 SiO ₂ 4,5 to 6.5 5.0 to 6.1 CaO 1.4 to 1,8 1.5 to 1.9 MgO 1,2 to 1.5 1.3 to 1.6

Table 1 continued component Albanian Fe-Ni-Cr ore Ni-leach mass%

Mn 0.3 to 0.4 0.3 to 0.4 P 0.04 0,04 ' with 0.05 0.05 At ₂ 0 0.07 0.08

During leaching, nickel and cobalt pass into the leachate, from which they are obtained by known methods. The solid residue of nickel leaching (see Table 1) in the dry state contains, in addition to 55 to 58 wt. % Fe also 2.3 to 2.8 wt. % Cr. While the treatment of the Ni-lime in a blast furnace is possible to obtain lean chromium iron (steel), this possibility is not of practical significance both for the problems associated with its manufacture and for the limited use of this material. Therefore, a substantial reduction in the chromium content is an essential prerequisite for the use of the Ni-lime to produce iron. However, all attempts in this direction have been unsuccessful so far, although many metallurgical and hydrometallurgical methods have been tested.

The metallurgical methods consisted of a complete reduction of iron and chromium oxides to metal in conjunction with further oxidation of the resulting Fe-Cr alloy by air or oxygen in a converter, a ladle, etc., while converting a portion of chromium together with a portion of iron into an etruscus. selective reduction of iron, with all chromium remaining in the slag. The deficiency of metallurgical methods is, besides the devaluation of a part of the iron and chromium content, mainly a completely insufficient degree of chromium removal.

The hydrometallurgical methods tested so far were mostly a variation of the classical method for the production of chromates and consisted of the alkaline-oxidative roasting of the Ni-leach in conjunction with the further leaching of the resulting roast with water. The disadvantage of these methods is, in addition to the relatively high chromium and alkali content in the solid residue after leaching, a particularly inefficient economy, which is caused by about 15 to 20 times lower chromium content in Ni-leach compared to conventional chromium ores.

It is known that certain trivalent chromium compounds, such as Cr (OH), and the like, can be oxidized to chromene in a solution of alkali hydroxides with oxidizing agents such as HgOg, PbOg, KMnO4, K4 / Fe (CN) g / etc., and that the same effect can be achieved using air or oxygen.

If chromium as Cr ₂ ° 3 ^{'then P-microbial} response ^ĥ difficult and requires higher pressures and temperatures. When it can be used as oxidation agents in addition to the above mentioned three agents also alkali content, which is characterized by the ability to cleave at temperatures higher bound kyalík as NaNO _2, NaNO ^ like.

Furthermore, it is known that CrgOy bound in the form of chromite FeO.CrgO- »can also be partially oxidized in an alkaline medium to chromate, either by means of NaClO or Na Fe (FeíCNJg) at elevated temperature at atmospheric pressure or by means of oxygen or air proportionally higher temperature and pressure.

All known attempts to utilize this interesting reaction have failed unsuccessfully due to the known complexity of the process due to the need to regenerate the oxidizing agents in the case of atmospheric pressure leaching, and due to the low reaction rate and mainly due to the lack of chromium leachability in higher temperatures and pressures.

Accordingly, it could not be expected that this known chromium ore treatment could be practically used to substantially reduce the chromium content of Ni-leach and similar materials.

In this situation, however, it has surprisingly been found that, under certain conditions, a reduction in the chromium content of Ni-leach and other materials below 0.2% by weight of chromium can be achieved by means of pressurized alkali-oxidative curing.

The principle of the invention is that the Ni-lime is mixed with a NaOH solution having a concentration of 200 to 600 g / l NaOH, preferably 390 to 460 g / l NaOH, with a concentration of 0 to 80 g / l CrO 2 and leaching. an additive or with an additive CaO which is added to the feed in an amount such that the molar ratio M CaO / SiO ₂ is 1, at a temperature of 200 to 360 ° C, preferably 330 to 350 ° C, for 15 to 120 minutes, preferably 30 to 60 minutes, wherein oxygen or air is introduced into the mash with a partial pressure of 0.98 to 5.88 MPa, preferably 1.96 to 4.9 MPa, higher than the vapor pressure of the used leaching solution at a given temperature .

This so-called pressurized alkali-oxidative leaching can be carried out under intensive stirring either batchwise in a stable autoclave with a stirrer, or preferably continuously in a flow-through autoclave. In this case, the chromium contained in the Ni-leach in the form of chromites is virtually quantitatively oxidized to CrO4 and passes into solution as sodium bromide. However, in addition to chromium, other Ni-leachable components leachable with NaOH, in particular SiOg and AlgOy, are leached. These substances are removed from the leachate by precipitation with CaO for 2 to 4 hours at a temperature above 100 ° C. sodium chromene is obtained in a known manner either by direct crystallization of an unconcentrated extract at -10 ° C or by crystallization of an extract concentrated above 650 g ^/ l ^, NaOH at a temperature of 0 to 30 ° C.

Chromium or chromium compounds are then obtained from sodium chromene by known methods. The mother liquor after crystallization was used for re-leaching. The solid residue from the pressurized alkaline-oxidative leaching of the Ni-leach, the so-called pressure-leach (see Table 2), reliably contains below 0.2 wt% Cr and 60 to 62 wt% Fe after filtration and washing. It is essentially a high-quality Fe-concentrate and, after drying and testing, is used directly for the production of iron.

Table 2

Pressure leaching from leaching Ni-leaching component without CaO with CaO, M CaO / SiOg = 1

Fe cel 60.0 to 62.0 54.0 to 56.0 Ni 0,30 to 0.35 0.28 to 0.32 Cr 0.04 to 0.10 0.03 to 0.08 What 0.02 0.02 SiO ₂ 1.50 to 2,0 4.70 to 6.1 ^A1 ° 2 0.40 to 0.70 0.35 to 0.70 CaO 1,5 to 1,8 7.5 to 8.1 MgO 1,5 to 1,8 1.5 to 1,8 Mn 0.4 to 0.50 0.4 to 0.50 P 0.02 to 0.03 0.02 to 0.03 WITH 0.02 to 0.03 0.02 to 0, 0'3 Ns ₂ 0 0,30 to 0.80 0.30 to 0.90 Absolutely in the same way it is possible to leach chromium directly from Fe-Ni-Cr ore and from Fe-Cr ores raw materials. In this case, nickel and cobalt quench method Caron to of pressure

Only the solid residue after the precipitation of nickel and cobalt is used as Fe-concentrate for the production of iron.

Thus, the invention allows complex processing of Fe-Ni-Cr ores or raw materials to nickel and cobalt, chromium or chromium and iron compounds, and complex processing of Fe-Cr ores or raw materials to iron and chromium or chromium compounds.

Example i

122 kg wet Ni-leach containing 18% moisture, which was produced by leaching of nickel and cobalt from Albanian Fe-Ni-Cr ore by the Caron method and contains in the dry state 55.0% by weight of Fe and 2.5% by weight of Cr, ee 700 liters of 460 g / ml CrOy return leach solution are mixed with the pump and then pumped through a pressure pump into a flow autoclave, which also serves as a heat exchanger. Oxygen or air with a partial pressure of 1.36 to 4.9 MPa higher than the leaching solution vapor pressure at said temperature is introduced into the autoclave together with the mash, so that the total pressure is 12.75 to 17.65 MPa. During the autoclave flow, the mash is gradually heated to a temperature of 330 to 350 ° C and maintained at this temperature for 30 to 60 minutes. After cooling, expanding and filtering the mash, after washing and drying the pressure leach,

88.5 kg of Fe-concentrate containing 62.0 wt.56 Fe and 0.10 wt.56 Cr. The yield of chromium is

96.5

Example 2

100 kg finely ground (90% below 0.1 mm) dried Albanian Fe-Ni_Cr ores containing 49 wt% X Fe, 1.05 wt $ 6 Ni, 2.5 wt.56 Cr and 5.5 wt. 56 SiOg is mixed with 725 L of 460 g of NaOH return solution and 40 g of NaCl and 5.2 kg of CaO. The mash is then pumped into a flow-through autoclave, where air or oxygen at a partial overpressure of 1.96-4.9 MPa is simultaneously introduced and gradually heated to 340-350 ° C. After sixty minutes of leaching at this temperature, after cooling, expanding and filtering the mash and after washing and drying, 80 kg of a pressure leach are obtained, from which, after nickel and cobalt removal by the Caron method, a Fe-concentrate containing 61.5% Fe is obtained. and 0.19 wt.56 Cr. The chromium yield is 94%.

Claims (4)

1. A process for removing chromium from low-nickel and chromium iron ores or chromium-containing iron ores or ferrous-nickel leach by pressure leaching, characterized in that the finely ground ore is leached with a sodium hydroxide solution above 200 gl ^- in an autoclave at a temperature above 200 ° C with the introduction of air or oxygen at an overpressure of more than 0.98 MPa, whereby the chromium is converted as a sodium chromate into a solution from which, after precipitation of impurities (SiO 2, Al 2 O 3) sodium chromate and this is further processed to chromium compounds or alloys or metal chromium. 2. The process of claim 1, wherein the ores are pre-leached with nickel and cobalt with an ammonium ammonium carbonate solution to obtain a ferrous nickel leach. Process according to Claims 1 and 2, characterized in that the solid residue after the precipitation of nickel and chromium, containing above 60% by weight of iron and below 0.2% by weight of chromium, is processed into pig iron or steel. 4. A method according to claim 1, 2 or 3, characterized in that lime is added to the ore or leach prior to pressure leaching in an amount such that the CaO / SiO2 molar ratio is equal to one in the autoclave charge.