Demineralization of brown coal

Claim 2

A brown coal demineralization process which includes the steps of forming the as mined brown coal into a slurry, grinding said slurry in the presence of aqueous sulphurous acid, subjecting said ground slurry to a froth flotation treatment in the presence of flotation reagents in which SO 2 is dissolved in the slurry to maintain acid concentration and withdrawing said brown coal for further downstream treatment.

Claim 3

The process of claim 1 in which said SO 2 is dissolved in the incoming slurry to the froth flotation treatment.

Claim 4

A demineralization process for low ranking coals such as brown coal which comprises the steps of forming the coal into a slurry, grinding said slurry in the presence of an aqueous acid selected from the group consisting of: a. hydrochloric b. sulphurous c. carbonic acids and d. mixtures of acids (a), (b) and (c), subjecting the ground slurry to a froth flotation treatment in the presence of flotation agents in which a respective gas selected from the group consisting of: a. chlorine b. sulphur dioxide c. carbon dioxide and d. mixtures of gases (a), (b) and (c) is dissolved in the slurry to maintain concentration of said acid, withdrawing separated coal particles and passing them to downstream treatment stages.

Claim 5

A demineralization process for low ranking coals such as brown coal which comprises the steps of forming the coal into a slurry, grinding said slurry in the presence of an aqueous acid selected from the group consisting of: a. hydrochloric b. sulphurous c. carbonic acids and d. mixtures of acids (a), (b) and (c), subjecting the ground slurry to a froth flotation treatment in the presence of flotation agents in which a respective gas selected from the group consisting of: a. chlorine b. sulphur dioxide c. carbon dioxide and d. mixtures of gases (a), (b) and (c) is dissolved in the slurry to maintain concentration of said acid, withdrawing separated coal particles and passing them to downstream treatment stages.

Claim 6

A process as claimed in claim 3 wherein said aqueous acid is added to the slurry prior to grinding.

Claim 7

A process as claimed in claim 3 wherein said aqueous acid is added to the slurry during grinding.

Claim 8

The process of claim 3 in which said acidic gas is introduced into the incoming slurry to said froth flotation treatment.

Claim 9

The process of claim 3 in which the acidic gas is introduced into froth flotation with compressed air.

Claim 10

The process of claim 3 in which the acid is hydrochloric acid and the gas is chlorine.

Claim 11

The process of claim 3 in which the acid is sulphurous acid and the gas is sulphur dioxide.

Claim 12

The process of claim 3 in which the acid is carbonic acid and the gas is carbon dioxide.

Claim 13

The process of claim 3 in which said acids are sulphuric acid and carbonic acid, said respective gases are sulphur dioxide and carbon dioxide, and the source of said acids and gases is the flue gases from a carbonizing plant in the downstream treatment.