received by the International Bureau on 22 October 2014 (22.10.2014) 1. A process of concentrating an aqueous suspension of solid particles, comprising the steps of,

introducing the aqueous suspension of solid particles into a vessel,

addition of at least one organic polymeric flocculant to the aqueous suspension of solid particles thereby forming flocculated solids,

allowing the flocculated solids to settle to form a compression zone, comprising a bed of sedi- merited solids in suspension at the lower end of the vessel,

flowing the sedimented solids from the vessel as an underflow stream,

in which.an effective amount of ultrasonic energy is applied to:

a) the bed of solids at the compression zone;

b) the sedimented solids in the underflow stream ; or

c) a recycle stream containing sedimented solids taken from either the underflow stream or the compression zone which are then recycled back to the vessel,

in which a chemical agent is applied to the aqueous suspension of solid particles, wherein the chemical agent is selected from oxidising agents, free radical agents and reducing agents.

2. A process according to any preceding claim, in which the ultrasonic energy applied to the bed of solids or the underflow will be in the range of 0.1 to 1000 Watts seconds/millilitres specific energy. 3. A process according to any preceding claim, in which the ultrasonic energy is applied at a frequency in the range of 1 KHz to 10 MHz, preferably between 5 KHz to 1 MHz, more preferably between 10 KHz to 100 KHz.

4. A process according to a preceding claim in which the ultrasonic energy is applied only to the bed of solids, to the underflow or a stream taken from the bed of solids all the underflow and recycled back to the vessel.

5. A process according to any preceding claim wherein the ultrasonic energy is applied by fixing ultrasonic transducers around the inside or outside of a sidewall of the vessel or to rakes at the height of the bed of solids, the transducers being connected to a control unit which can adjust the power output of the transducer to a desired power density.

6. A process according to any preceding claim in which the ultrasonic energy is applied to the bed of solids from a rake.

7. A process according to any preceding claim in which the chemical agent is applied to the bed of solids, the underflow or a stream taken from the bed of solids or the underflow and recycled back to the vessel.

8. A process according to any preceding claim in which an agent system is applied to the aqueous suspension of solid particles, wherein the agent system comprises i) at least one oxidising agent as the at least one active agent; and ii) at least one control agent. The at least one control agent should consist of iia) at least one activator component and/or iib) at least one sup- pressor component, in which the at least one activator component increases the activity of the oxidising agent and the suppressor component decreases the concentration or the activity of the activator component.

9. A process according to any preceding claim in which the vessel is a gravimetric thickener.

10. A process according to any preceding claim in which the aqueous suspension of solid particles comprises mineral particles.

11. A process according to any preceding claim in which the aqueous suspension of particles comprises red mud or tailings from metal extraction, acid leaching, coal, oil sands, mineral sands or other mining or mineral processing operations.

12. A process according to any preceding claim in which the organic polymeric flocculant is a non-ionic or anionic polymer that is either a synthetic polymer of intrinsic viscosity of at least 4 dl/g or a natural polymer.

13. A process according to any preceding claim in which the organic polymeric flocculant is selected from the group consisting of homopolymers of acrylic acid or salts thereof, homopoly- mers of acrylamide and copolymers of acrylamide and acrylic acid or salts thereof.

14. An apparatus suitable for concentrating an aqueous suspension of solid particles comprising

a vessel,

a means for introducing the aqueous suspension of solid particles into the vessel,

a means for introducing at least one organic polymeric flocculant to the aqueous suspension of solid particles, sufficient to form flocculated solids,

a means for allowing the flocculated solids to form compression zone, comprising a bed of sed- imented solids in the suspension at the lower end of the vessel,

a means for flowing the sedimented solids from the vessel as an underflow stream,

in which the apparatus comprises a means for applying ultrasonic energy to:

a) the bed of solids at the compression zone;

b) the sedimented solids in the underflow stream ; or

c) a recycle stream containing sedimented solids taken from either the underflow stream or the compression zone which are then recycled back to the vessel,

and in which the apparatus comprises a means for applying a chemical agent to the aqueous suspension of solid particles, wherein the chemical agent is selected from oxidising agents, free radical agents and reducing agents.