how to make brown limestone( calcium carbonnate powder) into a extra white color? can i use a bleaching powder?
In the limestone an impurity, such as iron ore, gives brown color. To get rid of it you must to apply technological process. You can try to use the acid, but in the process of reaction ions Fe3+ can be formed , which are also painted in brown color. FeO + 2H+ = Fe2+ + H2O Fe2O3 + 6H+ = 2Fe3+ + 3H2O Fe3O4 + 8H+ = 2Fe3+ + Fe2+ + 4H2O so you need to add some amount of zinc Zn + 2Fe3+ ---> Zn2+ + 2Fe2+ but Fe2+ is rapidly oxidized on air to Fe3+ Thus, to discolor limestone at home is almost impossible.