Patent Application
20080092693
In the drawings the same or similar parts have the same reference numbers.
The arrangement of the plant 10 is described by following the flow of material through the plant as follows:
Input of a sulphide concentrate, matte or alloy is fed to density adjust tank 12, the density of the material in the tank being adjusted with water via feed line or stream 30 and a reagent (acidic such as a spent electrolyte or alkali such as ammonia, sodium hydroxide, etc.), via feed line 32. The mass feed to the autoclave feed tank 14 is determined by appropriate instrumentation in feed line 34.
Feed tank 14 can receive process water via line 36 if the impact of the release of flash vapour via line 38 needs to be compensated for. Alternatively, the use of process water is invoked on a “need-to-have” basis. The feed tank may also receive a reagent, such as sulphuric acid or an alkali depending on the process intent, via line 40.
In operation, blended slurry received by feed tank 14 is pumped via line 42 into the autoclave first compartment. As the reaction proceeds and energy is released the temperature attains the set or desired temperature for this compartment. At temperatures above the set point the slurry is discharged from the first compartment as stream 44 to the flash tank 20 where a flash vapour component is released via line 38 either to atmosphere or to a heating duty elsewhere.
The flash tank underflow is drained to thickener 22 where a phase separation is achieved with the aid of a flocculant fed via stream 46. The overflow from the thickener is directed externally via line 48 in full or in part to the autoclave discharge tank 18, while the thickened solids are returned to the autoclave feed tank 14 via line 50.
In the design or modification of an existing autoclave, the first compartment is sized to achieve in excess of 40% typically 85-95% of the overall reaction extent. This implies that the thickener 22 overflow in stream 48 is often very similar in composition to the autoclave discharge stream 52 after flash.
The mean flow rate in the first and, in this case, ensuing compartments changes as follows:
Flash-recycle: {feed tank 34+process water 36+reagent 40} less flash vapour 38 FTR: . . . feed tank 34+process water 36+reagent 40 plus flocculant 46}, less {flash vapour 38+thickener overflow 56}
Thus the solids fraction retention time can be increased very significantly. Other factors such as oxygen gas mass transfer at the autoclave impellers may become rate limiting or the feed pumps on the feed tank 14 servicing the autoclave may reach their limit and thereby constrain further productivity gains.
Existing autoclaves originally fitted with a quench cooling system can in certain cases be increased in capacity by in excess of 100% whilst at the same time, in some cases, de-rated in pressure and temperature by employing the FTR process of the invention. The net feed rate 54 through the autoclave can be adjusted to suit the required mass flow and extraction simply by adjusting the volumetric flow of thickened solids stream 50 and overflow stream 56.
An example will now be given relating to the processing of nickel-copper sulphide mattes.
An autoclave system originally fitted with a quench cooling circuit was converted to incorporate the FTR process.
The flow sheet employed was similar to that in
The thickener overflow 48 gravitated in part along line 56 to the autoclave discharge tank while the balance was returned via line 58 to the feed tank. The solids plus some liquor making up stream 50 was also fed to feed tank 14.
In the autoclave, the slurry comprising stream 54 was further leached in the second and ensuing compartments and finally discharged as stream 52 into discharge tank 18 and flashed. The flash vapours from the discharge tank 18 were vented to atmosphere via line 60. The flash underflow from stream 52 and the thickener overflow 56 were blended in the discharge tank.
The chemistry in the autoclave can, in its simplified form, be represented by the following equations:
NiS+40==>NiSO4
Cu2S+H2S04+50==>2CuSO4+H20
Both these reactions generated significant energy and between 5 and 5.5 tonnes of steam per hour was released in the flash outlet 38.
The composition of various streams is given in tables 1A, 2A and 3A below.
The net flow through the autoclave is calculated by difference as stream 54 without compensating for density within the autoclave.
The net flow 54 is approximately 25% of the feed flow 34. However prior to this incorporation of this invention the feed flow was approximately
13.5 m3l/h. The slurry feed with this invention had increased by over 90% to 25.8 m3/h.
a. the flash from the autoclave first compartment is fed via a line 72 back into the feed tank 14;
b. the underflow in the feed tank is fed to the thickener 22. where, again, flocculant is added;
c. the solids fraction from the thickener is fed directly back to the feed tank, with the liquids fraction still being feed to the discharge tank 18; and
d. an acidic lixiviant is fed directly to the second compartment of the autoclave to compensate for the changed chemistry in the feed tank.
The invention is not limited to the precise details described above and shown in the drawings. Modifications may be made and other embodiments developed without departing from the spirit of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004/0082 | Jan 2004 | ZA | national |
| 2004/8476 | Oct 2004 | ZA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/ZA05/00002 | 1/7/2005 | WO | 00 | 8/21/2007 |
