Open-pit mining
After mining finishes, the mine area may undergo land rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to deep groundwater levels. Instead of returning the land to its former natural state, it may also be reused, converting it into recreational parks or even residential/mixed communities.
Kitchen utensil
There are several types of ceramic utensils.
Terracotta utensils, which are made of red clay and black ceramics. The clay utensils for preparing food can also be used in electric ovens, microwaves and stoves,
we can also place them in fireplaces. It is not advised to put the clay utensil in the 220-250
temperature oven directly, because it will break. It also is not recommended to place the clay pot over an open fire.
Clay utensils do not like sharp change in temperature. The dishes prepared in clay pots come to be
particularly juicy and soft – this is due to the clay’s porous surface. Due to this porous nature of the surface the clay utensils inhale aroma and grease. The coffee made in clay coffee boilers is very aromatic, but such pots need special care. It is not advised to scrub the pots with metal scrubs, it is better to pour soda water in the pot and let it stay there and afterwards to wash the pot with warm water. The clay utensils must be kept in a dry place, so that they will not get damp.