Manganese ferrite (MnFe2O4) Nanoparticles: From synthesis to application -A review

The surface reactivity of clay minerals remains challenging to characterize because of a duality of adsorption surfaces and mechanisms that does not exist in the case of simple oxide surfaces: edge surfaces of clay minerals have a variable proton surface charge arising from hydroxyl functional groups, whereas basal surfaces have a permanent negative charge arising from isomorphic substitutions. Hence, the relationship between surface charge and surface potential on edge surfaces cannot be described using the Gouy–Chapman relation, because of a spillover of negative electrostatic potential from the basal surface onto the edge surface. While surface complexation models can be modified to account for these features, a predictive fit of experimental data was not possible until recently, because of uncertainty regarding the densities and intrinsic pKa values of edge functional groups. Here, we reexamine this problem in light of new knowledge on intrinsic pKa values obtained over the past decade using ab initio...

Modeling the acid-base properties of montmorillonite edge surfaces

Activation mechanism of lead ions in the flotation of sulfidized azurite with xanthate as collector

Aqueous hexavalent chromium (Cr(VI)) treatment and chromium resource recovery toward Cr-containing wastes are of significant importance and necessity to both wastewater remediation and resource recovery. Herein, via mild photoreaction conditions with isopropanol (IPA) as an electron donor, a catalyst-free strategy for aqueous Cr(VI) extraction to form an insoluble polyhydroxy Cr(V) complex is developed for the first time. Aqueous Cr(VI) with concentration from 5 to 150 ppm can be efficiently extracted with high selectivity even in the presence of coexisting ions, and the total Cr concentration in residue solution can be as low as 0.5 ppm. The Cr resource could be efficiently recovered as pure Cr2O3 by calcinating the resulting Cr(V) precipitate. Outstanding extraction efficiency could be realized with various IPA concentrations (1.3-12.0 mol/L) by coordinately tuning the pH value to promote the formation of Cr(VI)-IPA ester. The formed ester undergoes intramolecular electron transition under visible light irradiation, resulting in a polyhydroxy solid-state Cr(V) intermediate complex. The controlled pH value blocks further reduction of Cr(V) to soluble Cr(III); thus the insoluble Cr(V) intermediate complex is stabilized thermodynamically under ambient conditions. Because of its electric neutrality property and the strong intermolecule interaction via hydrogen bonds, a dioxo-bridged di-nuclear Cr(V) complex {Cr2(μ-O)2(OH)4[OCH(CH3)2]2} is finally precipitated as the main product. Satisfactory extraction and recovery of Cr from chromium-plating wastewater and discarded stainless steel verify that this approach is ideal for both one-step purification of Cr(VI)-containing wastewater and selective resource recovery from Cr-containing solid wastes in practical application.

Selective and Efficient Photoextraction of Aqueous Cr(VI) as a Solid-State Polyhydroxy Cr(V) Complex for Environmental Remediation and Resource Recovery.

Over 90% of the global economy continues to use natural resources unsustainably. The linear “take-make-toss” approach to materials use still prevails over circular economy and industrial ecology ideas in practice. The shift to renewable energy is one step towards building an economy on more circular material flows. But the materials needed to decarbonize electricity and mobility are supplied by mining and extractives industries, places where impacts from natural resource extraction can be most severe. Manufacturers of wind turbines, photovoltaics, batteries and vehicles—critical technologies to the clean energy transition—still primarily rely on feedstocks and inputs from natural resources as opposed to waste for processing and production. Similarly, robust and complete end-of-life (EoL) management strategies are not well developed for these materials. This review synthesizes progress towards a circular economy—reducing impacts from resource extraction, metallurgy, manufacturing, and waste disposal, and resource recovery—in key materials needed to decarbonize electricity and mobility. Efforts to manufacture by principles of sustainable design to reclaim the recycling value of EoL product waste are complicated by new materials and increasingly complex composites. Dialog and collaboration about trends in materials use and waste flows that span extractive industry scientists and professionals to product designers and recyclers will be critical to spurring the technological and policy innovations needed to encourage more progress.

Progress towards a circular economy in materials to decarbonize electricity and mobility

NdFeB permanent magnet scrap is regarded as an important secondary resource which contains rare earth elements (REEs) such as Nd, Pr and Dy Recovering these valuable REEs from the NdFeB permanent magnet scrap not only increases economic potential, but it also helps to reduce problems relating to disposal and the environment Hydrometallurgical routes are considered to be the primary choice for recovering the REEs because of higher REEs recovery and its application to all types of magnet compositions In this paper, the authors firstly reviewed the chemical and physical properties of NdFeB permanent magnet scrap, and then carried out an in-depth discussion on a variety of hydrometallurgical processes for recovering REEs from the NdFeB permanent magnet scrap The methods mainly included selective leaching or complete leaching processes followed by precipitation, solvent extraction or ionic liquids extraction processes Particular attention is devoted to the specific technical challenge that emerges in the hydrometallurgical recovery of REEs from NdFeB permanent magnet scrap and to the corresponding potential measures for improving REEs recovery by promoting the processing efficiency This summarized review will be useful for researchers who are developing processes for recovering REEs from NdFeB permanent magnet scrap

Hydrometallurgical Recovery of Rare Earth Elements from NdFeB Permanent Magnet Scrap: A Review

The Chinese economy is in a critical period of continuous transformation of new and old kinetic energy and economic transformation and upgrading. Copper, the second largest strategic raw material, is still central to China’s economic development. As the major producer and consumer of electrical and electronic equipment (EEE), China’s production and consumption of refined copper is the largest in the world. Thus, it is necessary to forecast the supply and demand of China’s future copper. There is a huge gap between copper production and consumption in China, the current identified copper resources cannot meet copper consumption in the next five years, thus the import of copper will be more crucial for China’s future copper industry. Due to trade frictions, restriction on imports and other reasons, the import of copper from other countries will exist a lot of uncertainties. Hence, the domestic copper waste and scraps could be the suitable secondary resource for recycling copper in China. According to the grade and value of copper scraps, establishing quality standards and optimizing the disassembly process of the domestic Cu-bearing waste & scraps, and using the suitable method are the key to recycling the domestic copper scraps.

Shuo Liu

Papers

Hydrometallurgical Recovery of Rare Earth Elements from NdFeB Permanent Magnet Scrap: A Review

Recycling the domestic copper scrap to address the China’s copper sustainability

Recovery of chromium from chromium-bearing slags produced in the stainless-steel smelting: A review

Interfacial reaction between humic acid and Ca-Montmorillonite: Application in the preparation of a novel pellet binder

Spinel MnFe2O4 nanoparticles (MFO-NPs) for CO2 cyclic decomposition prepared from ferromanganese ores