A Comprehensive Review of Rare Earth Elements Recovery from Coal-Related Materials

Many studies have been published in recent years focusing on the recovery of rare earth elements (REEs) from coal-related materials, including coal, coal refuse, coal mine drainage, and coal combustion byproducts particularly fly ash. The scientific basis and technology development have been supported by coal geologists and extractive metallurgists, and through these efforts, the concept has progressed from feasibility assessment to pilot-scale production over the last five years. Physical beneficiation, acid leaching, ion-exchange leaching, bio-leaching, thermal treatment, alkali treatment, solvent extraction, and other recovery technologies have been evaluated with varying degrees of success depending on the feedstock properties. In general, physical beneficiation can be a suitable low-cost option for preliminary upgrading; however, most studies showed exceedingly low recovery values unless ultrafine grinding was first performed. This finding is largely attributed to the combination of small RE-bearing mineral particle size and complex REE mineralogy in coal-based resources. Alternatively, direct chemical extraction by acid was able to produce moderate recovery values, and the inclusion of leaching additives, alkaline pretreatment, and/or thermal pretreatment considerably improved the process performance. The studies reviewed in this article revealed two major pilot plants where these processes have been successfully deployed along with suitable solution purification technologies to continuously produce high-grade mixed rare earth products (as high as +95%) from coal-based resources. This article presents a systematic review of the recovery methods, testing outcomes, and separation mechanisms that are involved in REE extraction from coal-related materials. The most recent findings regarding the modes of occurrence of REEs in coal-related materials are also included.

Comparative study of low-grade banded iron ores for iron recovery

Two low-grade banded iron ores are evaluated as a potential source for meeting the iron/steel demand due to the scarcity of high-grade iron ores. The present study investigates the processing and enrichment of banded iron ores and their comparison with pure iron oxide and synthetic mixture. The feasibility of physical beneficiation, microwave processing, and carbothermal reduction is thoroughly investigated. A trace amount of magnetite in BHJ ore leads to an improved response of microwave exposure compared to pure iron oxide and mixture. Physical beneficiation was found futile in recovering iron values. The energy consumed during the microwave processing is calculated as 405.2 kWh/ton, whereas for conventional reduction is 223.7 kWh/ton. Significant iron enrichment was achieved through structural alteration of the ore. The microwave processing offered faster reduction kinetics and ferrite formation in a short duration. BHJ sample was found suitable for extracting iron values compared to BHQ using carbothermal reduction.

Siliceous Manganese Ore from Eastern India:A Potential Resource for Ferrosilicon-Manganese Production

Siliceous manganese ore, associated with the banded iron formation occurs in large volume in northern Odisha, India. It is a sub-grade ore containing 21% Mn, 60% SiO2 and 3% Fe, hence do not find any use and considered as waste. Such ore does not respond to any physical beneficiation techniques because of intricate microstructure and poor liberation of Mn-phase. It could only be up-graded to 32% Mn with 36% yield and 52% recovery by processing it through mineral separator followed by WHIMS. Siliceous manganese ore along with calcite and coke in appropriate ratio, when charged to a plasma reactor, a product with slag metal ratio of 2.5:1 was obtained within a period of 10 min. Electron probe micro-analysis of the metal confirmed it to be ferrosilicomanganese while the slag constitute of tricalcium silicate (C3S) with around 5% Mn in adsorbed state.

Characterization and beneficiation studies for the removal of iron from a china clay from India

A china clay sample from Jharkhand State, India, containing 65.0 wt.% SiO2, 22.7% Al2O3, 1.77% Fe2O3and 9.10% LOI was subjected to physical beneficiation and acid leaching studies to improve its quality. The clay was characterized by optical microscopy, XRD, and wet chemical analysis methods. Quartz and goethite are the two major impurities. High intensity magnetic separation removed only 10% of the total iron. Experiments with oxalic acid were carried out to establish the leaching kinetics of iron and the effects of acid concentration, time and temperature on iron leaching were also examined. The study demonstrated that ∼90% of total iron could be removed using 5% oxalic acid. The dissolution of iron from clay is best described by diffusion of ions through the product layer of constant size spherical particles. The activation energy of the leaching process over the temperature range was calculated to be 51.14 kJ/mol.

The Application of Magnesite Processing Technics

As one of the important refractory raw materials, the impurities of magnesite raw material had been strictly required. Magnesite processing methods can be divided into three categories, Physical beneficiation, chemical beneficiation and bacteriological beneficiation. And the flotation method is currently widely used in magnesite ore processing, but it also exists some problems.