How can we separate types of dal?

Winnowing is done to separate impurities from the pulses. As pulses are heavy and will stay in a place but the impurities like chaff will move away.

Winnowing is a farming method developed by ancient people for separating grain from the chaff.

It involves throwing the mixture into the air so that the wind blows away the lighter chaff. The heavier grains fall back down for recovery.