Wet-classifying method for recovery of carbon and iron-bearing particles

Claim 1

A method for treating an aqueous slurry of blast furnace flue dust containing between about 1 and 36 weight percent particles having a size consist of submicron up to 6.35 mm, about 80 weight percent of the particles are carbon and iron containing particles and about 20 weight percent of the particles are zinc and lead bearing particles and a substantial portion of the carbon and iron bearing particles are separated from the zinc and lead particles and are collected as a usable product, the method comprising: (a) straining the aqueous slurry of blast furnace flue dust to make a size separation at about 4 mm whereby all the relatively large foreign matter and the carbon and iron bearing particles larger than 4 mm are separated as a strainer overflow from substantially all the particles which are smaller than 4 mm and which are collected as a strainer underflow containing between 3 and 20 weight percent of the particles in the aqueous slurry of blast furnace flue dust, (b) separating substantially all the carbon and iron bearing particles from the foreign matter in the strainer overflow, (c) treating the strainer underflow of step (a) in at least one hydrocyclone operating at above atmospheric pressure wherein a substantial portion of the carbon and iron bearing particles which have a size larger than about 5 microns and not more than about 10 weight percent of the water in the strainer underflow are separated as a hydrocyclone underflow from substantially all the zinc and lead bearing particles having a size smaller than about 5 microns and not less than about 90 weight percent of the water in the strainer underflow as a hydrocyclone overflow, (d) passing the hydrocyclone overflow of step (c) to storage, and (e) passing the carbon and iron bearing particles in the hydrocyclone underflow to a filter to remove a portion of the water contained therein, as a filtrate and recovering the carbon and iron bearing particles as a filter cake, (f) passing the filtrate to waste, and (g) passing the filter cake to a preparation plant.

Claim 2

A method for treating an aqueous slurry of blast furnace flue dust containing between about 1 and 36 weight percent particles having a size consist of submicron up to 6.35 mm, about 80 weight percent of the particles are carbon and iron containing particles and about 20 weight percent of the particles are zinc and lead bearing particles and a substantial portion of the carbon and iron bearing particles are separated from the zinc and lead particles and are collected as a usable product, the method comprising: (a) straining the aqueous slurry of blast furnace flue dust to make a size separation at about 4 mm whereby all the relatively large foreign matter and the carbon and iron bearing particles larger than 4 mm are separated as a strainer overflow from substantially all the particles which are smaller than 4 mm and which are collected as a strainer underflow containing between 3 and 20 weight percent of the particles in the aqueous slurry of blast furnace flue dust, (b) separating substantially all the carbon and iron bearing particles from the foreign matter in the strainer overflow, (c) treating the strainer underflow of step (a) in at least one hydrocyclone operating at above atmospheric pressure wherein a substantial portion of the carbon and iron bearing particles which have a size larger than about 5 microns and not more than about 10 weight percent of the water in the strainer underflow are separated as a hydrocyclone underflow from substantially all the zinc and lead bearing particles having a size smaller than about 5 microns and not less than about 90 weight percent of the water in the strainer underflow as a hydrocyclone overflow, (d) passing the hydrocyclone overflow of step (c) to storage, and (e) passing the carbon and iron bearing particles in the hydrocyclone underflow to a filter to remove a portion of the water contained therein, as a filtrate and recovering the carbon and iron bearing particles as a filter cake, (f) passing the filtrate to waste, and (g) passing the filter cake to a preparation plant.

Claim 8

The method of claims 5 or 6 in which a sufficient amount of lime is added to the strainer underflow to adjust the pH to between about 9.0 and 9.4.