Drying kinetics of Philippine nickel laterite by microwave heating

ABSTRACT

In this study, microwave heating was used to dry nickel laterite, which contains significant quantities of free water, crystal water, and hydroxy water. The results show that the main phase of crystal water is Ca₃Al₆Si₁₀O₃₂(H₂O)₁₃, and the main phases of hydroxy water are FeO(OH) and Mg₅(Al, Cr)AlSi₃O₁₀(OH)₈. The microwave drying process of nickel laterite can be divided into two stages: the removal of free water and the coupled removal of free water, crystal water, and hydroxy water. The effect of particle size and microwave power output were studied, and these indicate that the drying time and specific energy consumption decrease with increasing particle diameter and microwave power. The effective diffusivity and activation energy were calculated, and these are larger in the second stage than that in the first stage. The activation energies are 27.66 and 32.80 W/g for the first and second stages, respectively. The phase transition of the product, schematic drying mechanism, and feasibility analysis of the microwave drying process are also discussed.

KEYWORDS:

• Activation energy
• energy consumption
• microwave drying
• nickel laterite
• XRD analysis

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [Grant No. 51234010].