Bleaching Experiment Of Pyrophyllite Powder

Pyrophyllite is a dioctahedral 2:1 clay mineral, which is a hydrous aluminiumsilicate with Si4Al2O10(OH)2 and has good chemical stability, resistance to heat and mechanical processing properties. However, the raw pyrophyllite mineral contains iron oxides and organic compounds as the mainly impurity, which deteriorate the purity and whiteness of pyrophyllite seriously and restrict their applications. To upgrade the technique level of mineral processing industry and transform the resource superiority to an economic one, we have to develop suitable bleaching technologies and a series of deep processing products.This dissertation is base on the structural characteristics of pyrophyllite, and develops the pyrophyllite reduction bleaching process: Bleaching experiments on pyrophyllite powder were carried out by the method of acid as soaking agent and Na₂S₂O₄ as reducer, which can improve the whiteness of pyrophyllite. Some factors that influence iron leaching from pyrophyllite were investigated in our experiments, such as kinds of acids, acid concentration, temperature, soaking time, dosage of Na₂S₂O₄, dosage of oxalic acid and so on. And the aim of this work is trying to find out a less complex, cost-effective and eco-friendly approach for iron removal from pyrophyllite powder. The results show that: Hydrochloric acid, acetic acid or oxalic acid which was as a soaking agent, could be used to play a good bleaching effect. A great number of experiments were performed to the optimal technological parameters as follows: the hydrochloric acid concentration was 20%(V/V), the temperature was 80℃, the soaking time was 2h, the dosage of pyrophyllite powder and Na₂S₂O₄ and oxalic acid was 40:2:1. After bleaching, the pyrophyllite powder whiteness was increased from 69.5% to 84.1%. This process of brightening pyropyllite has the characteristics of simple and lower costs.