Perspective on pH adjustment in hydrometallurgical recycling of valuable metals from waste
Zhu Suiyi, Jian Wang, Huang Yuhong, Wang Ying, Zhang Yuxin, Qin Jiabao, Jiancong Liu, Yao Jinlu, Ji Meichun
Abstract
pH adjustment was considered a simple step in the hydrometallurgy process, but its complicated operation was ignored in the past. In some industrial applications, the leachate pH was slowly adjusted by a diluted alkaline solution, with the defects of doubling the leachate volume and causing droplet hydrolysis/coagulation. Up to date, promising routes have been developed for rapid pH adjustment, especially in sealed high-temperature/pressure vessels. New routes emerged in some redox/decomposition reactions of nitrate/urea and organics. Such reactions did not start and/or were slow at room temperature but started spontaneously at high temperatures to generate/consume free H + . This induced pH adjustment in a rapid and homogeneous way.