Shengen Zhang

Rare earth elements recycling from waste phosphor by dual hydrochloric acid dissolution

This paper is a comparative study of recycling rare earth elements from waste phosphor, which focuses on the leaching rate and the technical principle. The traditional and dual dissolution by hydrochloric acid (DHA) methods were compared. The method of dual dissolution by hydrochloric acid has been developed. The Red rare earth phosphor (Y0.95Eu0.05)2O3 in waste phosphor is dissolved during the first step of acid leaching, while the Green phosphor (Ce0.67Tb0.33MgAl11O19) and the Blue phosphor (Ba0.9Eu0.1MgAl10O17) mixed with caustic soda are obtained by alkali sintering. The excess caustic soda and NaAlO2 are removed by washing. The insoluble matter is leached by the hydrochloric acid, followed by solvent extraction and precipitation (the DHA method). In comparison, the total leaching rate of the rare earth elements was 94.6% by DHA, which is much higher than 42.08% achieved by the traditional method. The leaching rate of Y, Eu, Ce and Tb reached 94.6%, 99.05%, 71.45%, and 76.22%, respectively. DHA can decrease the consumption of chemicals and energy. The suggested DHA method is feasible for industrial applications.

Challenges in legislation, recycling system and technical system of waste electrical and electronic equipment in China.

Waste electrical and electronic equipment (WEEE) has been one of the fastest growing waste streams worldwide. Effective and efficient management and treatment of WEEE has become a global problem. As one of the worlds largest electronic products manufacturing and consumption countries, China plays a key role in the material life cycle of electrical and electronic equipment. Over the past 20 years, China has made a great effort to improve WEEE recycling. Centered on the legal, recycling and technical systems, this paper reviews the progresses of WEEE recycling in China. An integrated recycling system is proposed to realize WEEE high recycling rate for future WEEE recycling.

Supply and demand of some critical metals and present status of their recycling in WEEE

New development and technological innovations make electrical and electronic equipment (EEE) more functional by using an increasing number of metals, particularly the critical metals (e.g. rare and precious metals) with specialized properties. As millions of people in emerging economies adopt a modern lifestyle, the demand for critical metals is soaring. However, the increasing demand causes the crisis of their supply because of their simple deficiency in the Earths crust or geopolitical constraints which might create political issues for their supply. This paper focuses on the sustainable supply of typical critical metals (indium, rare earth elements (REEs), lithium, cobalt and precious metals) through recycling waste electrical and electronic equipment (WEEE). To illuminate this issue, the production, consumption, expected future demand, current recycling situation of critical metals, WEEE management and their recycling have been reviewed. We find that the demand of indium, REEs, lithium and cobalt in EEE will continuously increasing, while precious metals are decreasing because of new substitutions with less or even without precious metals. Although the generation of WEEE in 2014 was about 41.9 million tons (Mt), just about 15% (6.5 Mt) was treated environmentally. The inefficient collection of WEEE is the main obstacle to relieving the supply risk of critical metals. Furthermore, due to the widespread use in low concentrations, such as indium, their recycling is not just technological problem, but economic feasibility is. Finally, relevant recommendations are point out to address these issues.

Shape and size effects on layered Ni/PZT/Ni composites magnetoelectric performance

This paper presents the magnetoelectric (ME) effect in trilayered Ni/PZT/Ni composites which is related to their size and shape. The ME composites with the same interfacial areas but different geometrical shapes have different ME voltage coefficients. Longitudinal resonant modes in the rectangular and triangular trilayered ME composites were studied. One should choose optimized size, shape and working frequency of the ME composites in order to gain the maximum ME effect. This study plays a guiding role for trilayered ME composites design for real applications.

Simple model of the magnetoelectric effect in layered cylindrical composites

A simple model of the magnetoelectric (ME) effect in cylindrical layered composites is presented. The cylinder is replaced by the effective layered plate structure with effective length, Leff, thickness t and height h. In the axial coupling mode, the effective magnetic field acts along the length direction (Leff). However, in the vertical coupling mode, the effective magnetic fields act in two directions simultaneously, one along the thickness direction (normal, t) and the other along the effective height (tangential, Leff) direction, respectively. Experimental results and theoretical analysis indicated that the cylindrical layered composites ME voltage coefficient is much higher compared with that of the layered plate.

Electro-deposition current density effect on Ni/PZT layered magnetoelectric composites performance

This paper considers the magnetoelectric (ME) effect in Ni/PZT layered ME composites that is related to the preferred crystallographic orientation of electro-deposited Ni layers. The Ni electro-deposition rate increases with applied cathodic current density. High (1 0 0) texture in the Ni layer was obtained at either low or high current densities, which improves the ME composites performance. It is advantageous to increase the current density, while trying to avoid hydrogen evolution during electro-deposition to reduce the number of pinhole defects.

Multiplied magnetoelectric effect in multi-faceted magnetoelectric composite

A four-faceted magnetoelectric (ME) composite consisting of one cuboid bonded Terfenol-D composite and four plates of Pb(Zr,Ti)O3 (PZT) was fabricated. The ME voltage coefficients were measured along the length direction of the composite when PZT plates were parallelly or serially connected. Results show that the ME voltage coefficient remains almost the same when increasing the number of PZT in parallel mode. By contrast, the ME voltage coefficient increases multiplicatively with the increasing of the number of PZT in serial mode. This multi-faceted structure scheme offers an effective approach to improving ME effect and downsizing the ME devices.

Effects of pre-strain and baking parameters on the microstructure and bake-hardening behavior of dual-phase steel

In a typical process, C-Mn steel was annealed at 800°C for 180 s, and then cooled rapidly to obtain the ferrite-martensite microstructure. After pre-straining, the specimens were baked and the corresponding bake-hardening (BH) values were determined as a function of pre-strain, baking temperature, and baking time. The influences of pre-strain, baking temperature and baking time on the microstructure evolution and bake-hardening behavior of the dual-phase steel were investigated systematically. It was found that the BH value apparently increased with an increase in pre-strain in the range from 0 to 1%; however, increasing pre-strain from 1% to 8% led to a decrease in the BH value. Furthermore, an increase in baking temperature favored a gradual improvement in the BH value because of the formation of Cottrell atmosphere and the precipitation of carbides in both the ferrite and martensite phases. The BH value reached a maximum of 110 MPa at a baking temperature of 300°C. Moreover, the BH value enhanced significantly with increasing baking time from 10 to 100 min.

Wide magnetic field range of Ni-P/PZT/Ni-P cylindrical layered magnetoelectric composites

The Ni-P/PZT/Ni-P cylindrical layered magnetoelectric (ME) composites were prepared by electroless deposition. The Ni-P layer has an amorphous nanocrystalline structure. The ME effect in the axial mode of the Ni-P/PZT/Ni-P cylindrical layered composites is similar to that of Ni/PZT/Ni. The Ni-P/PZT/Ni-P composite has lower bias magnetic field of 120 Oe to induce a maximum αE,A and 0.5 kOe to generate αE,A linear increase at the resonance frequency, which may be related to the high permeability of the Ni-P layer. This discovery contributes to the ME devices miniaturization and expands the magnetic field detection range at both low and high magnetic fields.

Peak divergence in the curve of magnetoelectric coefficient versus dc bias magnetic field at resonance region for bi-layer magnetostrictive/piezoelectric composites

Magnetoelectric (ME) coefficient dependence on the bias magnetic field at resonance frequencies for the bi-layered bonded Terfenol-D/Pb(Zr,Ti)O3 composite was investigated. The resonance frequency decreases first and then increases with the bias magnetic field (HDC), showing a “V” shape in the range of 0 ∼ 5 kOe. Below the resonance frequency, the pattern of ME coefficient dependence on the HDC shows a single peak, but splits into a double-peak pattern when the testing frequency increases into a certain region. With increasing the frequency, a divergent evolution of the HDC patterns was observed. Domain motion and ΔE effect combined with magnetostriction-piezoelectric coupling effect were employed to explain this experimental result.