Mechano-chemical modification of carbon adsorbent for purification of phosphoric acid
A widely used method of combined wet-process phosphoric acid (WPA) purification from fluorine, silicon, aluminium and iron compounds is the technology with the application of adsoption purification. Carbon materials are the most acceptable precursors for manufacturing a high-effective adsorbent which possesses significant exchange capacity for the mentioned compounds. The application of mechanochemistry is one of the most important directions for improving carbon adsorbent technology.
In this work the influence of mechano-chemical modification of the activated carbon of BAC on WPA purification efficiency is investigated. It has been shown that the adsorbents with the maximum content of oxygen- containing surface sites have the greatest affinity for impurities. Samples underwent mechano-chemical modification at the flow of oxygen-air mixture in the roll-annual vibrating mill VM-4. It has been found by means of potentiometric titration and infrared spectroscopy that functional groups in a wide range of acidity were formed after mechano-chemical treatment. Concentrations of surface sites increase up to 5 to10 mmole/g and exceed 2-3 times those for chemically treated samples. The choice of active liquid or gaseous media under mechano-chemical activation allows to control adsorbent surface property. Mechano-chemical reaction between the carbon material and oxygen proceeds according to a radical mechanism. Active radical particles were formed during homolytic rupture of carbon-carbon bonds in mainly aliphatic intercrystalline bridges. These particles interact with oxygen and moisture of air. This results in surface groups formation with various acidity. The degree of purification from the given compounds by means of mechano- chemical activation increases from 85 to 95 mass %.
And in conclusion: I’d like to say that this problem is the theme of my diploma. I have been working at it during 2 years and I am going to continue it in future. I thank my scientific supervisor Smirnov N.N.