Fluid treatment apparatus and process
Liquid treatment apparatus comprises at least two chambers being first and second chambers through which a fluid can flow. The two chambers are separated by at least one choke nozzle which has an entrance in the first chamber and an exit in the second chamber. The choke nozzle ( 1 ) comprises a converging section at its entrance ( 3 ), a throat section ( 4 ), a backward-facing step ( 5 ) immediately after the throat section ( 4 ), and an exit section at its exit ( 6 ) wherein the exit section ( 6 ) diverges from the step ( 5 ). Similarly constructed mixing nozzles ( 1 ) may be included in the apparatus. The apparatus is especially useful in processes requiring a gas to be entrained in a fluid so that the gas is in the form of very small bubbles that do not tend to coalesce and flash off such as in the dissolution of gold and other precious metals from ore in the removal of arsenic from an ore.
1. A process for enhancing chemical or physical reactions occurring in processes in which a slurry and a gas are contacted such that at least a component of the gas partakes in a physical or chemical reaction with at least one component of the slurry with the gas in the form of bubbles entrained in the slurry, wherein the size of the gas bubbles is reduced by utilizing choked flow, the process comprising passing the slurry from a first chamber to a second chamber through a choke nozzle comprising a converging section, a throat section, a backward-facing step immediately after the throat section and an exit section wherein the directional flow, angular velocity, centrifugal acceleration and straight line acceleration of the slurry create conditions providing cavitation consequent on choked flow through the choke nozzle wherein the process includes diffusing a gas in the slurry and generating bubbles in the slurry that accelerate through the throat section to cause the bubbles to implode and form multiple smaller bubbles, the process being characterized in that the gas is introduced through one or more gas inlets having their axes extending transversely at an offset in a generally tangential direction relative to slurry flow so that a swirling action of diffusing gas in the slurry results.
2. A process as claimed in claim 1 in which the process forms part of a process for separating gold and other metals from ore in which oxygen or air is diffused within a slurry of milled ore, water and calcium cyanide or sodium cyanide so as to sufficiently oxidize the ore for reduced cyanide consumption, improved metal leaching or to facilitate flotation of the gold particles from the ore.
3. A process as claimed in claim 1 in which the converging section, the throat and the exit section of the choke nozzle are each of circular shape in cross-section, and the exit section diverges.
4. A process as claimed in claim 1 in which the slurry and gas are passed through at least one mixing nozzle selected from before they enter a choke nozzle; after they leave a choke nozzle, and both before and after a choke nozzle; and wherein a mixing nozzle has a converging section at its entrance, a throat section, a backward-facing step immediately after the throat section, and an exit section at its exit which opens into a downstream chamber.
5. A process as claimed in claim 1 in which in which the converging section of a choke nozzle has a cone angle of from 1 to 35 degrees.
6. A process as claimed in claim 5 in which the cone angle is from 15 to 30 degrees.
7. A process as claimed in claim 1 in which the backward-facing step of a choke nozzle extends radially outwards beyond the throat section by 3 to 10% of the diameter of the throat.
8. A process as claimed in claim 7 in which the backward-facing step extends radially outwards beyond the throat section by from 4 to 8%.
9. A process as claimed in claim 1 in which the exit section of the choke nozzle diverges with a cone angle of from 1 to 8 degrees.
10. A process as claimed in claim 9 in which the exit section diverges with a cone angle of from 2 to 8 degrees.
11. A process as claimed in claim 1 in which a diverging exit section to a choke nozzle has additional successive backward-facing steps along the exit section.