GB2087257A

GB2087257A - Method and arrangement for continuous leaching of solid material

Info

Publication number: GB2087257A
Application number: GB8129190A
Authority: GB
Original assignee: Elkem ASA
Current assignee: Elkem ASA
Priority date: 1980-09-26
Filing date: 1981-09-28
Publication date: 1982-05-26
Also published as: NO151900B; NO151900C; FR2491087A1; AU7565581A; DE3138156A1; DK424881A; JPS5787803A; FI812963L; NO802851L; SE8105649L

Abstract

Soluble components in solid material are dissolved continuously in a column comprising one or more stages where the stages are separated by means of perforated plates (2). Solid material and liquid can pass each other countercurrently or cocurrently. The solid material is supplied continuously or periodically to the top of the column at (3) and sinks downwards in the column either by settling through the holes in the plate (or plates) or by hydraulic movement of the current of liquid. The solid material can after the leaching be subjected to a washing process in the lower part of the column or in a separate washing equipment. The ready leached solid material is discharged continuously or batchwise from the bottom of the column, possibly through a separate washing unit. Both the charging and discharging of the solid material can be governed by computer. The leach liquid is pumped into the column from the bottom for countercurrent leaching and from the top for cocurrent leaching. The leach liquid moves in both cases through the length of the column and through the solid material reacting with the latter before it is piped off from the top of the column for countercurrent leaching and from the bottom of the column for cocurrent leaching. <IMAGE>

Description

SPECIFICATION Method and arrangement for continuous leaching of solid material The invention relates to a method and equipment for continuous leaching of solid material by means of a liquid. By such leaching the soluble components in the solid material will be transferred to the liquid phase.

There are known several methods for leaching of solid material with liquids. As example can be mentioned leaching in containers with stirring equipment followed by filtration. This method requires however that the solid material has been crushed to small particle sizes. It is also known that the solid material can be leached in stationary bed where the liquid is sprayed on the bed or pumped upwards through the bed from the bottom of the equipment. Such method is however depending on relatively course material with comparatively narrow size distribution in order to prevent clogging and allow good distribution of the leach liquid. This method also requires that the material is sieved to remove the smallest particles.

It is further known to leach solid material in fluidised bed. This process requires small particle size and low density of the solid material and requires as well crushing as careful sieving operation, and the liquid must in addition be of certain specifications if the required and necessary degree of fluidisation shall be obtained.

The known systems which are described above do also require much space and equipment and are often limited to special particle sizes and types of solid material. Method which are carried out with coarse material do also require much labour, and methods which are carried out with fine material require as mentioned crushing and complicated filtering operations.

The methods as a rule limited to stationary batch leaching or cocurrent leaching, that is leaching where the solid materials and the liquid are flowing in the same direction or where the solid material is stationary.

The inventors have now found a method and an apparatus which can be utilised as well for countercurrent leaching as for co-current leaching, further it is also possible to treat a series of different particle sizes in the equipment and the method is specially of advantage in connection with treatment of coarser particle sizes as for instance coarsely crushed materials. As well liquid as solid material flow continuously through the equipment.

By the method according to the invention the reactions are carried out with a vertical column comprising one or more stages and the stages are separated by perforated plates. The solid material is supplied continuously or periodically to the top of the column and sinks downwards within the column by settling through the holes in the plates or by hydraulic movement from the flow of liquid. Already reacted solid material can be discharged periodically from the bottom of the column after determined time intervals by means of a valve arrangement which can be governed by computer. The leach liquid is piped into the column from the bottom by countercurrent leaching and from the top by cocurrent leaching.The leach liquid does in both cases move all the length of the column through the solid material and react with the latter before being piped away from the top of the column by countercurrent leaching and from the bottom by cocurrent leaching.

The perforated plates within the column will keep the stages separated and effect redistribution of the liquid.

Washing stages for washing of already reacted solid material can be built in the bottom of the column. Already treated and discharged solid material is removed from the bottom portion of the column for instance by hydraulic transport. The transport of the solid material for further utilisation or deposit can be carried out by hydraulic transport in a closed pipe system. In cases where the column comprises few or only one single stage, other arrangement for redistribution of the liquid phase must be built into the column in order to secure homogeneous distribution of the liquid in the solid material.

The column can be designed for a series of reaction conditions and number of stages, and the flow rate of solid material and liquid can be adjusted within a large area independently and according to need.

Solid material is as mentioned supplied to the top of the column which can be divided into more stages by means of perforated plates, and the solid material will move periodically or continuously downward through the column from stage to stage with defined retention times in each stage. The length liquid is as mentioned pumped in at the bottom orthetop ofthe column and moves upwards in countercurrent with the solid material with overflow at the top, respectively downwards in cocurrent with the solid material and with outlet at the bottom. After defined time intervals the solid material is transported downwards in the column to the next stage.This is effected by opening the bottom valve and discharging a certain amount of solid material, and the rest of the solid material within the column will then either settle through the holes or be transported by means of a liquid impulse cocurrently to the solid material.

The plates which separate the stages are equipped with a number of perforations of a size which allows transport of the material through the holes.

The number and size of the holes must be adjusted to the solid material in question. The most important task of the plates is to redistribute the leach liquid and effect a good distribution of same. The apparatus has no movable parts and can be adjusted to a series of conditions and demands as regards variation in particle sizes and retention time for liquid as well as solid material. Filtering of the residue is as mentioned not necessary.

The residue from the column will always carry along some leach liquid as well on the surface as within the pores and this liquid must be washed out by displacement by a washing liquid, usually water.

The washing can take place as well countercurrently as cocurrently, it is however of advantage to use cocurrentwashing when the leach liquid has a higher specific weight than the washing liquid. The washing will be most effective when the liquid flow profile is sharply downwards in the column and the leach liquid and the wash liquid are minimally intermixed. The residue can be stationary while the washing liquid is supplied continuously to the top of the section or the bottom of the section and be let out from the bottom or from the top of the column respectively.

In order to promote a fuller understanding of the above and other aspects of the invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Figure I shows a column for countercurrent leaching and countercurrent washing, Figure II shows a column for cocurrent leaching without washing, and Figure IIl shows a column for countercurrent leaching with separate cocurrent washing in the bottom.

In Figure 1 the column itself which in this case is operated countercurrently and comprises six leaching stages and two washing stages is indicated by 1. The perforated plates which separate the different leaching steps are indicated by 2. The solid material which shall be treated is supplied to the top of the column as indicated by 3. There can be employed a belt conveyor for supply as indicated by 4, and the movement direction of the material is indicated by arrows. The leach liquid is supplied by the lowermost perforated plate as indicated by 5.

Dosage arrangements take care of continuous or periodic supply according to desire. The leach liquid is supplied from a storage tank and the direction of flow is indicated by arrows. The solid material sinks or is as mentioned conducted periodically downwards within the column and can eventually be subjected to a washing process in the lower part of the column for instance in two washing stages.

These washing stages are created by insertion of an extra plate 6 below the lowermost of the ordinary plates 2. The solid residue will collect in the bottom of the column as indicated by7 and is discharged periodically by means of a discharge arrangement as indicated by 8 and falls into a tank 9 with discharge arrangement 9a from where it can eventually be removed continuously or for instance by means of hydraulic transportation means. The leach liquid for washing stage is supplied at 10. The wash liquid will in this case intermingle with the leach liquid.

The washing liquid can also be used for hydraulic transportation of the solid residue which is removed from the tank 9. If the washing water is to be separated from the leach liquid, the washing section and the leach section can be separated by a valve and the washing can be effected cocurrently below this valve in one or more stages. The liquid phase which contains the dissolved components is re moved from the column by overflow at the top as indicated by 11.

In Figure II which shows cocurrent leaching with out washing the leaching liquid is supplied at 12, while the enriched mother lye is removed at 13, 14 is a residue tankforthe solid material, and the liquid for hydraulic transportation of the residue out of the tank is supplied at 15. The discharge arrangement is indiacated at 16.

In Figure Ill which shows countercurrent leaching with cocurrentwashing 17 is the washing section which comprises one or more washing stages. The leaching liquid is supplied at 18 and removed at 19 while the washing liquid is supplied at 20 and removed at 21. The solid material is removed from the washing section by the discharge arrangement 22 and conducted to the residue tank 23 from where it is removed by the discharge arrangement 24, possibly by hydraulic transport.

Examples Aluminium was leached from anorthosit by means of a hydrochloric acid solution. The onorthosit contained 30,9%AI203,15%CaO,1,1 1,1%Fe2O3 and 0,5%MgO, and the leaching was carried out with a 7 molar hydrochloric acid. There was used a countercurrent column with 5 stages and a height of 3 metres. The anorthosit was present in particle sizes of 0,5 - 3,3 mm, and it was supplied batchwise to the top of the column from which it moved downwards in the column in the course of the reaction time which was in total 21 hours, that is 4,2 hours per stage. The acid reacts with the aluminium mineral and dissolves it. The acid which was preheated to 100 Cwas pumped in near the bottom of the column at a rate of 5 litres per hour and removed by overflow at the top of the column.The flow rate of the mineral through the column and consequently the retention time is governed by the discharge in the bottom which in this case was 1,5 kg/hour and was carried out periodically by means of a pneumatic sleeve valve which was governed by a time relay.

The residue was collected in the tank at the bottom of the column and was pumped out by hydraulic transportation, in this case water, when the tank was full. The mother lye contained after the leaching 36 g/l Al and the concentration was 1,0 molar HCI. The aluminium recovery was 90%.

Example 2 Anorthositas in Example 1 was leached in cocurrent column as in Figure II with 7 molar hydrochloric; acid preheated to 100C. The column consisted of 4 stages and was 2,5 m high and 0,1 m in diameter.

The anorthosit and the hydrochloric acid was supplied continuously to the top of the column and moved concurrently downwards in the column. The retention time for the anorthosit was 27 hours and for the acid 1,6 hours. The temperature within the column was maintained by circulation of boiling water in heat casings mounted on the outside of the column. At the top of the column there was arranged a reflux cooler for condensation of hydrochloric acid vapour from the lye. The bottom of the column consisted of a small section with an outlet on the side equipped with a sieve on the inside. The lye was removed through this outlet pipe and conducted in rising pipes along the column in order to equalise the hydrostatic pressure of the liquid within the column and thus maintain the column filled with liquid.The rate and retention time of the mineral was governed as described in Example 1. When the receiving tank for the residue was filled after drainage of accompanying lye, the residue was pumped hydraulically out of the system.

The already lye contained 38,8 g/l Al and the concentration of the acid was 0,36 molar. The recovery of aluminium was 82%.

Example 3 Anorthosit as in Example 1 was leached with 7 molar HCI in countercurrent column equipped with washing stages (Figure Ill). The already leached material was conducted from the leaching section to the washing section at a rate of 1 kg/hour. When the washing section had been filled with material the washing water was piped in at the top art a rate of 4 1/hour and removed from the bottom. The washing liquid which at the start was about 0,1 molar HCI was returned to the process. The washing water contained traces of Al-, Fe- and Ca- salts, totally about 1,5 g/l. There was employed about 0,51 washing water per kg residue and this was as mentioned recirculated. When the washing interval was finished the supply of liquid was stopped and the washed residue was conducted to the collecting container.

The washed residue contained 3,7% Al203,64%SiO2, 2%CaO, 0,3%MgO and 0.65%Fe203.

Claims

1. A method of continuous leaching of soluble components from solid material in which leaching takes place in a column comprising one or more stages where each stage is separated by means of a perforated plate and where the solid material and the liquid can pass each other concurrently as well as cocurrently.

2. A method as claimed in Claim 1 in which the solid material is subjected after leaching to a washing process in a lower part of column.

3. A method as claimed in Claim 1, in which the solid material is subjected after leaching to a washing process in a separate washing section.

4. A method as claimed in Claim 1,2 or 3 in which supply and discharge of solid material can take place continuously or batchwise and may be governed by computer.

5. A method as claimed in Claims 1,2,3 or 4 in which the solid residue is conducted from the bottom of the column optimally through a separate washing section, to a separate tank from where it can be removed continuously or batchwise by hydraulic transportation.

6. A column for carrying out the method of any one of Claims 1 to 5 in which the solid material is supplied at the top of the column and discharged near its bottom, while the leaching liquid is supplied to or near the bottom of the column and discharged at or near the top of the column.

7. A column as claimed in Claim 6, in which the washing section is arranged below the lowermost perforated plate in the leaching section.

8. A column for carrying out the method of any one of Claims 1 to 5 where the solid material and the liquid move in the same direction in which the solid material is supplied to the column at its top and discharged from its bottom portion, the leaching liquid being also supplied at the top and discharged from the column at the lowest part of the column.

9. A column as claimed in claim 6 or 8 in which the lower part of the column comprises a washing section with one or more stages where the residue from the leaching process is washed countercurrently.

10. A column as claimed in Claims 6 or 8 in which a separate washing section is arranged below the column, and in which the residue is washed cocurrently.

11. A column as claimed in Claims 6 or 8, in which a separate washing section is arranged below the column and in which the residue is washed countercurrently.

12. A column as claimed in Claims 6 or 8, in which the residue is retained in a stationary state in the washing section during the washing operation while the washing liquid is supplied continuously to the top of the section and removed from the bottom.

13. A column as in Claims 6 or 8 in which the residue is maintained stationary while the washing liquid is supplied continuously from the bottom of the section and removed from the top.

14. A method of continuous leaching of soluble components from solid material substantially as herein described with reference to the accompanying drawings.

15. A column for continuous leaching of soluble components from solid material substantially as herein described with reference to the accompanying drawings.