Enhancement on Synthesis of Boehmite Through a Precarbonization-assisted Hydrogen Peroxide Route in Highly Alkaline Sodium Aluminate Solutions

Abstract

Hydrogen peroxide (H 2O 2) precipitation from sodium aluminate (SA) solution at close-ambient temperature is an efficient method to synthesize boehmite and its derived alumina with high surface area, but the precipitation yield of Al 2O 3 is usually below 50% in highly alkaline SA solutions. Here the synthesis of boehmite is enhanced through a precarbonization-assisted H 2O 2 route in highly alkaline SA solutions. It is found that the crystal structure of the precipitation product is evidently influenced by the precipitation conditions. As the precipitation temperature increases from 273 to 325 K, a small amount of gibbsite by-product is formed. As the aging temperature increases from 301 to 333 K, the crystallinity of boehmite decreases and part of the boehmite dissolves due to an increase in the pH value. Based on the above results, a precarbonization-assisted H 2O 2 route is proposed to obtain pure boehmite with more complete recovery of Al 2O 3 from highly alkaline SA solutions. The route includes a controllable precarbonization step of SA solutions with a molar ratio of Na 2O to Al 2O 3 higher than 2 : 1, followed by the H 2O 2-precipitated step with a molar ratio of H 2O 2 to Al 2O 3 less than 7 : 1. Because of its facile operation conditions, no extraneous impurity, time saving and a possible recycle of the filtrate, the route has great potential to be an alternative method for preparation of boehmite and its derived alumina.