A method used to concentrate the ore of lead. Name the process.
Lead and zinc ores (usually sphalerite, ZnS) often occur together and may also contain silver, copper and gold. The ore has first to be separated from clays and other silicates ('gangue') after which the lead ore and the zinc ore are separated.
The process used is froath flotation a succession of stages each delivering a greater concentration of the lead ore. The ore, containing gangue (which typically contains 3-8% lead) is ground with water to a particle size similar to that of fine sand (<0.25 mm). This is then mixed with water and a frothing agent (a detergent) and is violently agitated by air to form a fine suspension with a froth of bubbles on the top. The process is carried out in a series of tanks. As the lead and zinc minerals are less readily wetted than the gangue, they adhere to the air bubbles which are carried to the surface. The rock particles sink and the lead and zinc ores are skimmed off.
Then the lead ore is separated from the zinc ore. A chemical called a depressant is added which is soluble in water (for example, zinc sulfate) and the zinc ore sinks and the lead ore is skimmed off. Later, a chemical such as copper(II) sulfate is added and the zinc ore now floats and is skimmed off.
The lead ore concentrate from the flotation tanks now contains about 50% lead and ca 0.1% of silver, a relatively small but valuable amount.
Lead and zinc ores (usually sphalerite, ZnS) often occur together and may also contain silver, copper and gold. The ore has first to be separated from clays and other silicates ('gangue') after which the lead ore and the zinc ore are separated.
The process used is froath flotation a succession of stages each delivering a greater concentration of the lead ore. The ore, containing gangue (which typically contains 3-8% lead) is ground with water to a particle size similar to that of fine sand (<0.25 mm). This is then mixed with water and a frothing agent (a detergent) and is violently agitated by air to form a fine suspension with a froth of bubbles on the top. The process is carried out in a series of tanks. As the lead and zinc minerals are less readily wetted than the gangue, they adhere to the air bubbles which are carried to the surface. The rock particles sink and the lead and zinc ores are skimmed off.
Then the lead ore is separated from the zinc ore. A chemical called a depressant is added which is soluble in water (for example, zinc sulfate) and the zinc ore sinks and the lead ore is skimmed off. Later, a chemical such as copper(II) sulfate is added and the zinc ore now floats and is skimmed off.
The lead ore concentrate from the flotation tanks now contains about 50% lead and ca 0.1% of silver, a relatively small but valuable amount.
