How do you make chalk from cassava?

The food cassava is the starchy root of the cassava shrub.
It must be prepared and cooked correctly or it is toxic.
The method required depends on the size and variety of the root. Most methods involve allowing the peeled, or peeled and ground root to steep in water, and the water is then discarded. The discarded water contains toxins.
One method is the mixing of the ground cassava with water into a thick paste, which is then left in a thin layer exposed to the air for at least 5 hours.