AU4375001A - Hydrochloric acid leaching and regeneration method - Google Patents

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Actual Inventor Iluka Resources Limited Brian Anthony O'Brien Address for service is: WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 r Attorney code: WR Invention Title: "Hydrochloric Acid Leaching and Regeneration Method" Details of Associated Provisional Application No: PQ8026 The following statement is a full description of this invention, including the best method of performing it known to me:- Hydrochloric Acid Leaching And Regeneration Method Field Of The Invention The present invention relates to a hydrochloric acid leaching and regeneration method. More particularly, the present invention relates to the use of hydrochloric acid in leaching and the regeneration of hydrochloric acid from aqueous iron chloride solutions.

Background Art The cost of fresh hydrochloric acid is significant, so the commercial use of such as a leaching agent requires a cost-effective method of regenerating and recovering the hydrochloric acid.

Regeneration of hydrochloric acid is used in the steel industry, where steel is cleaned, or'pickled', in a hydrochloric acid solution before galvanising. However, the volumes of ilmenite leach solution produced by leaching commercial quantities of ilmenite are commonly far higher than those produced in pickling processes. Accordingly, capital costs mean that the application of technologies developed for regeneration of pickling solutions to regeneration of ilmenite leach solutions is not necessarily straightforward.

Further, conventional ilmenite leach processes start with a hydrochloric acid concentration of about 20% w/w, and endeavour to consume as much of the hydrochloric acid as possible, to avoid sending unused acid to regeneration.

This adds significantly to leach times, and thus production costs.

The object of the present invention is to overcome the abovementioned problems of the prior art, or at least provide an alternative thereto.

The applications of the present invention include regeneration of hydrochloric acid from the metal chloride solution that results from leaching predominantly iron from ilmenite, and the regeneration of pickling solution produced from treating the surface of steel with hydrochloric acid, although they are not limited thereto.

The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure Of The Invention In accordance with the present invention there is provided a hydrochloric acid leaching and regeneration method comprising the steps of: 15 leaching a substance in a leach solution containing hydrochloric acid and iron chloride at elevated temperature to produce a spent leach solution; introducing hydrochloric acid and/or hydrogen chloride gas into the spent leach solution; allowing precipitation of solid metal chlorides and regeneration of hydrochloric acid, thereby producing a regenerated leach solution; separating the solid metal chlorides from the regenerated leach solution; pyrohydrolysing the solid metal chlorides to produce hydrogen chloride gas, water and metal oxides; and recycling the hydrogen chloride gas into the spent leach solution.

-4- The regenerated leach solution may be recycled to the leaching step.

In one form of the invention, after the introduction of the hydrochloric acid and/or hydrogen chloride gas into the spent leach solution, the spent leach solution is cooled to allow precipitation of solid metal chlorides and regeneration of hydrochloric acid.

Preferably, the hydrochloric acid and/or hydrogen chloride gas introduced into the spent leach solution substantially comprises the hydrogen chloride gas generated by the pyrohydrolysis of the solid metal chlorides. Preferably still, the hydrochloric acid and/or hydrogen chloride gas introduced into the spent leach solution virtually exclusively comprises the hydrogen chloride gas generated by the pyrohydrolysis of the solid metal chlorides One or more of the above steps may be performed concurrently.

o The method of the present invention may, after introducing hydrochloric acid and /or hydrogen chloride gas into the spent leach solution and before cooling the spent leach solution to allow precipitation of solid metal chlorides and regeneration of hydrochloric acid, comprise the additional step of: evaporating water from the spent leach solution to increase the concentration of hydrochloric acid.

The method of the present invention may, after separating the solid iron metal chlorides from the regenerated leach solution and before pyrohydrolysing the solid metal chlorides to produce hydrogen chloride gas, water and metal oxides, comprise the additional.step of: removing surface liquor and water of crystallisation from the solid metal chlorides by heating.

In one form of the invention, the metal chlorides are predominantly iron (11) chlorides.

In one form of the invention, the substance is ilmenite. Preferably, the leach is conducted at a temperature in excess of 1000C. Preferably still, the leach is conducted at a temperature of approximately 1080C.

Preferably, the spent leach solution is cooled to below 300C. Preferably the solution is cooled to approximately 250C or below. In one form of the invention, the solution is cooled to approximately 200C.

Preferably, the leach solution comprises between 5 and 25% metal chlorides, which are predominantly iron (11) chloride, and between 25 and 10 hydrochloric acid, the remainder being predominantly water, where all percentages are expressed by weight. Preferably still, the leach solution comprises between and 16% metal chlorides, which are predominantly iron (11) chloride, and between and 14 hydrochloric acid, the remainder being predominantly water, where all percentages are expressed by weight.

In a highly preferred form of the invention, the leach solution comprises approximately 17% HCI, 13% metal chlorides, which are predominantly iron (11) chloride and 70% H 2 0, where all percentages are expressed by weight.

In one form of the invention, the solid metal chlorides are pyrohydrolysed by reaction with a mixture of gases resulting from the combustion of a portion of predominantly hydrocarbon fuel.

Brief Description Of The Drawings The present invention will now be described, by way of example only, with reference to one embodiment thereof, and the accompanying drawings in which:- Figure 1 shows a schematic hydrochloric acid leaching and regeneration flow diagram in accordance with the embodiment.

-6- Best Mode(s) For Carrying Out The Invention In Figure 1 there is shown a schematic diagram for hydrochloric acid leaching of ilmenite, and regeneration of the hydrochloric acid according to the embodiment.

A portion of ilmenite 10 is thermally conditioned 12 before being leached 14 in a leach solution containing approximately 17% wlw hydrochloric acid and 13% wlw FeC1 2 at approximately 106 to 110 0 C, for a period of approximately 3.5 hours.

The mixture so produced is then filtered 16. The filter cake is washed, and the washings combined with the filtrate to produce a solution 18 containing approximately 5.3% w/w HCI and 26.7% w/w metal chlorides, predominantly FeCI 2 Washed filter cake 19 is then calcined 20 to produce synthetic rutile 21.

To control a build-up of minor elements that do not crystallise with the FeCI 2 a bleed of filtrate 15 may be employed. The bleed stream 17 so produced may be of the order of up to 5 to 10% by weight of filtrate.

S.The solution 18 is then cooled before being passed to an absorber 22 where hydrogen chloride gas 24, generated as will be described subsequently, is introduced thereto. The solution is then passed to a crystallisation phase 26, where crystals of metal chlorides, predominantly hydrated iron(ll) chloride, form as the temperature decreases. These crystals are allowed to settle, and the bulk of the liquor, comprising approximately 17% w/w HCI and 13% w/w metal chlorides, predominantly FeCI 2 is tapped off from above the crystals and passed to a holding tank 28 for use in subsequent leaching 14. The mixture of crystals and remaining liquor are sent to a first crystal holding tank 30, with a second crystal holding tank 32 holding the liquor and crystals from a previous cycle.

The mixture of crystals and liquor from the previous cycle is passed to a filtration stage 34 and the filtrate, comprising approximately 17% w/w HCI and 13% w/w metal chlorides, predominantly FeC1 2 is stored in the holding tank 28 for use in subsequent leaching 14.

Filter cake 36, generated by the filtration stage 34, comprising largely FeC1 2 .4H 2 0 and surface water, is then passed to a pyrohydrolysis stage 40, to -7generate iron oxide and hydrogen chloride gas. The pyrohydrolysis stage involves the introduction of air, and of water and carbon dioxide gases formed by the combustion of fuel in a burner 42, to achieve a temperature of approximately 850C in the pyrohydrolyser. Hydrogen chloride gas is generated according to the following equation: 4FeCI 2 4 H20(g) O2(g)- 2Fe 2 0 3 8HCI(g) The iron oxide is dumped, whilst the hydrogen chloride gas, along with the unreacted combustion gases, is passed to the absorber 22, by way of a heat exchanger 44. Hydrogen chloride gas is absorbed by the cooled solution 18, whilst the unreacted combustion gases are passed to the atmosphere via a scrubber 50. The heat exchanger 44 helps control the temperature in the absorber 22 as the absorption efficiency decreases with the rising temperature of the absorption medium.

The amounts in streams 36 and 17 are adjusted such that the HCI gas generated in the pyrohydrolyser is approximately equal to the HCL consumed in the leach.

The pyrohydrolyser unit may be provided in the form of a rotary kiln, such that it ,acts as both a reaction chamber and a heat exchanger to cool the exhaust gas down to approximately 150 0

C.

Examples The following examples, each comprising several experiments, are intended to assist in the understanding of the reaction parameters of the present invention.

It must be appreciated that the following description of the examples is not to limit the generality of the above description of the invention.

Example 1 (Small scale leach efficacy) Thermally conditioned ilmenite (80g), water (87g), FeCI 2 .2H 2 0 (49g) and 32% w/w hydrochloric acid (155g) were mixed in a three necked flask to produce a -8solution of 17% w/w hydrochloric acid, 13%FeCI 2 and 70% water. According to Schimmel's (Schimmel, JAmerican Chem Soc, (1952),Volume 74,page 4689) data on the HCI/FeCI 2

/H

2 0 system, the mixture so formed is saturated at 200C.

The mixture was maintained at a temperature between 105 and 1070C for a period of three hours and the filtered and washed leached product calcined.

By way of comparison, thermally conditioned ilmenite (80g), water (137g) and 32% w/w hydrochloric acid (233g) were mixed in a three-necked flask to produce a solution of 20% w/w hydrochloric acid and 17.8% solids. The mixture was maintained at a temperature between 105 and 107°C for a period of three hours and the filtered and washed leached product calcined.

As Table 1, below, shows, despite the significant reduction in hydrochloric acid added, the leach results from the system containing FeCl 2 were comparable to conventional acid leaching.

Table 1 Table 1 f r r r c (Percentages) TiO 2 FeT FeO MnO A1 2 0 3 Si0 2 ThO 2 Feed ilmenite 58.9 24.7 7.6 1.33 0.9 0.71 115 94.7 2.1 0.06 0.80 1.02 86 17%HCI 13% FeC 2 93.6 2.82 0.10 0.82 1.08 83 Example 2 (Large scale leach efficacy) A fluidising column was charged with 1.989 kg of thermally conditioned ilmenite, 1.474 kg of FeCI 2 .4H 2 0, 3.842 kg of 32% w/w hydrochloric acid and 1.916 kg of water. The solution component of the mixture had a density of 1.205 gmL 1 and analyses showed 218 gL 1 free hydrochloric acid, and 74.5 gL 1 total iron, and 21.6% solids. These analyses equated to 18.1% HCI and 14% FeCl 2 against the expected 17 and 13% respectively.

At 30 minutes from the start of the leach, the liquor had attained a temperature of 101°C, and most of the leach was run between 106 and 1070C. The total leach time was 3.5 hours.

At the conclusion of the leach, 7.339 kg of liquor was recovered. Hot wash water (500 g) was poured onto the solids remaining in the wash vessel and removed by suction to recover 617 g of displaced interstitial liquor that was added to the previously recovered liquor to give a total liquor recovery of 7.956 kg. For ease of description, this liquor will be referred to as liquor A. Table 2, below, shows the changes in concentrations, based on analyses and weights.

Table 2 Start Change End Percentage

H

2 0 5063 +169 5232 66.6 HCI 1229 -685 544 6.9 FeCI 2 940 +828 1768 22.5 FeCI 3 0 +250 250 3.2 Other CI- 0 +62 62 0.8 Assays showed the liquor A to contain 104 gL 1 free HCI and 142 gL 1 total iron.

The density was 1.298 gmL The 6.9% HCI translates to 90 gL 1 free HCI. And the 1768 g FeCI 2 and 250 g FeCI 3 translate to 863 g of Fe, or 143 gL 1 Fe. The product liquor was cooled to 3 0 C, and no crystallisation was observed.

Example 3 (Crystallisation) A sample of 150 g of the liquor A was introduced into a glass cylinder sitting on a top load balance. Hydrogen chloride gas was introduced into the base of the cylinder via a glass tube until a mass increase of 13.3 g was recorded. The requisite mass increase was estimated to correspond to an increase in the acid concentration of the liquor to 13 -14%.

It was noted that bubbles introduced at the base of the cylinder were absorbed before they reached the surface of the liquor. A temperature increase to 550C was noted, and no crystallisation was observed immediately upon cessation of the introduction of the hydrogen chloride gas.

The liquor was allowed to cool. When the temperature had reached 30 0

C,

crystallisation was observed. The liquor was then cooled to 20 0 C, and allowed to stand for 20 minutes before being filtered. Hard green and fine yellow crystals were collected (26.7 although recovery was by no means quantitative.

The filtrate, which will be subsequently described as liquor B, was then analysed to contain 216 gL 1 free HCI and the density was 1.243 gmL 1 translating to 17.4 %w/w HCI. Table 3 details the changes in concentrations of key components, based on the assumption that the collected crystals were FeCI 2 .4H 2 0, where X represents the mass of FeCI 2 4 Table 3 Liquor A Change Result Liquor (After filtration)

H

2 0 99.9 99.9 99.9- 0.576X HCI 10.35 +13.3 23.65 23.65 FeCl2 33.75 33.75 33.75-X FeCI 3 4.8 4.8 4.8 Other CI- 1.2 1.2 1.2 Total 150 163.3 163.3-1.567X Accordingly, solving for X shows 17.3 g of FeC 2 or 27 g of FeCI 2 .4H20, close to predicted behaviour.

Example 3 A sample of ilmenite of composition shown in Table 4 is reacted with a leach solution as shown in Table 5, at a temperature of approximately 105 to 107°C for a period of about 3.5 hours. Table 4 shows the changes in the concentrations of -11 the components of the ilmenite, and Table 5 the changes in the concentrations of the components of the leach solution.

Table 4 Species Concentration Mass Change Leached solids (kg) (kg) Mass TiO 2 55.6 8760 0 8760 92 FeO 41.4 6523 -6241 282 3 Others 3 474 0 474 Total 100 15757 9516 100 5 During the leach, iron (II) oxide reacts with hydrochloric acid according to the following equation: FeO 2HCI FeCI 2

+H

2 0 Accordingly, if 6241 kg of FeO react, 6319 kg of HCI is consumed, and 11000 kg of FeC 2 and 1560 kg of H 2 0 produced, as shown in Table Table Species Concentration Mass Change End of leach (kg) (kg) Mass

H

2 0 70 41402 +1560 42962 65.7 HCI 17 10054 -6319 3735 5.7 FeCI 2 13 7689 +11000 18689 28.6 Total 100 59146 65386 100 Table 6 details the changes in composition of the spent leach liquor upon addition of wash water and hydrogen chloride gas.

-12- Table 6 End of Add wash Product mixture After filtration Species leach water and mass Species HCl mass mass (kg) HCIg) (kg) (kg)

H

2 0 42962 +4681 47643 62.3 41402 HCI 3735 +6319 10054 13.2 10054 17 FeC 2 18689 18689 24.5 7689 13 Total 65386 76386 100 59145 100

S.

The product mixture containing 13.2% HCI and 24.5% FeCI 2 will become saturated at about 55°C, and when cooled to 20 0 C, 11000 kg of FeCI2 and the associated 6241 kg of waters of crystallisation are removed from solution.

In a conventional leach, where the starting liquor is 20% and HCI and 80% water, the free acid at the end of the leach is about as shown in Table 7, below.

Table 7 Species Concentration Mass Change End of leach (kg) (kg) Mass

H

2 0 80 31697 +1560 33257 72.5 HCI 20 7924 -6319 1605 FeC 2 0 +11000 11000 24.0 Total 100 36921 45862 100 (+wash water) 4681 50543

S

S S In the conventional acid leach, the leach phase is necessarily longer due to the lower hydrochloric acid concentration driving the reaction. The conventional leach sends 50543 kg of liquor to the preconcentrator.

-13- As can be seen from the preceding tables, the method of the present embodiment maintains a higher hydrochloric acid concentration in the leach phase, so the leach may be effected more rapidly. Further, only 17241 kg of crystals are sent to pyrohydrolysis, with surface liquor of perhaps 3000 kg. This surface liquor would contain only about 510 kg of HCI (3000 x 0.17), as opposed to the 1605 kg of HCI sent to the preconcentrator in the conventional leach circuit.

It is envisaged that the method of the present invention may be applied to the regeneration of acid solutions used in the pickling of steel and the upgrading of ilmenite that has not been thermally conditioned. In the latter case, rather than converting the ilmenite into synthetic rutile, an ilmenite of low grade, eg 54% TiO 2 may be converted into a high-grade ilmenite, eg 62% TiO 2 predominantly by leaching iron oxides from the ilmenite. The upgraded ilmenite might then be S fed into a Becher ilmenite reduction kiln.

15 Modifications and variations such as would be apparent to the skilled addressee Sare considered to fall within the scope of the present invention.

o

Claims (19)

1. A hydrochloric acid leaching and regeneration method comprising the steps of: leaching a substance in a leach solution containing hydrochloric acid and iron chloride at elevated temperature to produce a spent leach solution; introducing hydrochloric acid and/or hydrogen chloride gas into the spent leach solution; allowing precipitation of solid metal chlorides and regeneration of hydrochloric acid, thereby producing a regenerated leach solution; 10 separating the solid metal chlorides from the regenerated leach solution; pyrohydrolysing the solid metal chlorides to produce hydrogen chloride gas, water and metal oxides; and °oooo recycling the hydrogen chloride gas into the spent leach solution.

2. A method according to claim 1 wherein the regenerated leach solution is recycled to the leaching step.

3. A method according to claim 1 or claim 2 wherein, after the introduction of the hydrochloric acid and/or hydrogen chloride gas into the spent leach solution, the spent leach solution is cooled to allow precipitation of solid metal chlorides and regeneration of hydrochloric acid.

4. A method according to any one of the preceding claims wherein the hydrochloric acid and/or hydrogen chloride gas introduced into the spent leach solution substantially comprises the hydrogen chloride gas generated by the pyrohydrolysis of the solid metal chlorides.

A method according to claim 4 wherein the hydrochloric acid and/or hydrogen chloride gas introduced into the spent leach solution virtually exclusively comprises the hydrogen chloride gas generated by the pyrohydrolysis of the solid metal chlorides.

6. A method according to any one of the preceding claims wherein, after introducing hydrochloric acid and /or hydrogen chloride gas into the spent leach solution and before cooling the spent leach solution to allow precipitation of solid metal chlorides and regeneration of hydrochloric acid, the method comprises the additional step of: evaporating water from the spent leach solution to increase the concentration of hydrochloric acid.

7. A method according to any one of the preceding claims wherein, after the of separating the solid iron metal chlorides from the regenerated leach solution and before pyrohydrolysing the solid metal chlorides to produce hydrogen chloride gas, water and metal oxides, the method comprises the additional step of: removing surface liquor and water of crystallisation from the solid metal chlorides by heating.

8. A method according to any one of the preceding claims wherein one or more of the above steps are performed concurrently.

9. A method according to any one of the preceding claims wherein the metal chlorides are predominantly iron (11) chlorides.

A method according to any one of the preceding claims wherein the substance is ilmenite.

11.A method according to claim 10 wherein the leach is conducted at a temperature in excess of 100°C. -16-

12. A method according to claim 11 wherein the leach is conducted at a temperature of approximately 108 0 C.

13. A method according to any one of claims 10 to 12 wherein the spent leach solution is cooled to below 300C.

14. A method according to claim 13 wherein the solution is cooled to approximately 250C or below.

A method according to claim 14 wherein the solution is cooled to approximately 200C.

16. A method according to any one of claims 10 to 15 characterised in that the 10 leach solution comprises between 5 and 25% metal chlorides, which are Spredominantly iron (11) chloride, and between 25 and 10 hydrochloric acid, the remainder being predominantly water, where all percentages are expressed by weight.

17. A method according to claim 16 characterised in that the leach solution comprises between 10 and 16% metal chlorides, which are predominantly iron (11) chloride, and between 20 and 14 hydrochloric acid, the remainder °being predominantly water, where all percentages are expressed by weight.

18. A method according to claim 17 characterised in that the leach solution comprises approximately 17% HCI, 13% metal chlorides, which are predominantly iron (11) chloride and 70% H 2 0, where all percentages are expressed by weight.

19. A method according to any one of the preceding claims wherein the solid metal chlorides are pyrohydrolysed by reaction with a mixture of gases resulting from the combustion of a portion of predominantly hydrocarbon fuel. -17- A hydrochloric acid leaching and regeneration method substantially as described herein with reference to Figure 1. Dated this Seventh day of May 2001. Iluka Resources Limited Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant .o