Mechanochemical reduction of nickel oxide with continuous hydrogen flow

Abstract

Metal oxides reduction is one of the most important steps in metal production, where hydrogen-based metallurgy would significantly reduce greenhouse gas emissions from this emission-intensive process. By using mechanical energy, mechanochemistry enables the reduction of metal oxides at lower temperatures or even room temperature, which could significantly reduce energy loss due to heat dissipation in metal production at high temperatures. However, increased water partial pressure from hydrogen-based reduction leads to limited reaction rates. Herein, we demonstrate a mechanochemical method for the reduction of nickel oxide, adopting a ball milling system under continuous hydrogen flow. Nickel oxide can be mechanochemically reduced at room temperature or with mild heating (100 °C) for faster water removal. 88 wt% of nickel could be reduced after 10 h of milling. Efficient mechanochemical reduction benefits from the generation of abundant oxygen vacancies, increased surface area, continuously renewed particle surface, and constant removal of moisture. Compared to traditional metal oxide reduction methods, hydrogen-based mechanochemical reduction offers a low-temperature metallurgical pathway with no direct carbon emissions.