The invention relates to apparatus and a process for mixing a gas/vapour with a process liquid comprising a material and a carrier liquid. The apparatus comprises a passage (10) of polygonal cross section having an inlet (14), an outlet (16) for a process liquid comprising the material, and a nozzle (24) for introducing supersonic gas/vapour at a mixing zone (42) in a single plane.

An additive delivery system may incorporate a cartridge system, including a container cap and a reservoir assembly that provides for storage of an additive. The container cap includes a mixing nozzle for mixing of the additive with a base fluid as the base fluid flows from the base fluid container through the cartridge. A one-way valve prevents backflow of base fluid and/or mixed base fluid/additive from an area downstream of the mixing nozzle such that the base fluid supply remains in a pure state.

The invention relates to apparatus and a process for mixing a gas/vapour with a process liquid comprising a material and a carrier liquid. The apparatus comprises a passage (10) having an inlet (14), an outlet (16) for a process liquid comprising the material, and an inlet (24) for introducing supersonic steam at a mixing zone (42). The profile of the mixing zone (42) can be varied to optimise mixing.