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The current uncertainty in the global supply of rare earth elements (REEs) necessitates the development of novel extraction technologies that utilize a variety of REE source materials. Herein, we examined the techno-economic performance of integrating a biosorption approach into a large-scale process for producing salable total rare earth oxides (TREOs) from various feedstocks. An airlift bioreactor is proposed to carry out a biosorption process mediated by bioengineered rare earth-adsorbing bacteria. Techno-economic assessments were compared for three distinctive categories of REE feedstocks requiring different pre-processing steps. Key parameters identified that affect profitability include REE concentration, composition of the feedstock, and costs of feedstock pretreatment and waste management. Among the 11 specific feedstocks investigated, coal ash from the Appalachian Basin was projected to be the most profitable, largely due to its high-value REE content. Its cost breakdown includes pre-processing (leaching primarily, 77.1%), biosorption (19.4%), and oxalic acid precipitation and TREO roasting (3.5%). Surprisingly, biosorption from the high-grade Bull Hill REE ore is less profitable due to high material cost and low production revenue. Overall, our results confirmed that the application of biosorption to low-grade feedstocks for REE recovery is economically viable.

Several test patterns integrated with microheaters are used to analyze and characterize the cross-plane and in-plane Seebeck coefficients for ErAs: lnGaAs/ lnGaAlAs superlattices with different carrier concentrations. The results show that a heterostructure thermionic emission takes place in the cross-plane direction, which can be proved to be an after effect of the decrease in the Seebeck coefficient with increasing carrier concentrations.

The 3ω technique and time-domain thermoreflectance (TDTR) are two experimental methods capable of measuring the cross-plane thermal conductivity of thin films. We compare the cross-plane thermal conductivity measured by the 3ω method and TDTR on epitaxial (In0.52Al0.48)x(In0.53Ga0.47)1-xAs alloy layers with embedded ErAs nanoparticles. Thermal conductivities measured by TDTR at low modulation frequencies (∼1 MHz) are typically in good agreement with thermal conductivities measured by the 3ω method. We discuss the accuracy and limitations of both methods and provide guidelines for estimating uncertainties for each approach. [ABSTRACT FROM AUTHOR]

We characterize cross-plane and in-plane Seebeck coefficients for ErAs:InGaAs/InGaAlAs superlattices with different carrier concentrations using test patterns integrated with microheaters. The microheater creates a local temperature difference, and the cross-plane Seebeck coefficients of the superlattices are determined by a combination of experimental measurements and finite element simulations. The cross-plane Seebeck coefficients are compared to the in-plane Seebeck coefficients and a significant increase in the cross-plane Seebeck coefficient over the in-plane Seebeck coefficient is observed. Differences between cross-plane and in-plane Seebeck coefficients decrease as the carrier concentration increases, which is indicative of heterostructure thermionic emission in the cross-plane direction. [ABSTRACT FROM AUTHOR]

The comparison of the 3[omega] technique and time-domain thermoreflectance (TDTR) on epitaxial [([In.sub.0.52][Al.sub.0.48]).sub.x][([In.sub.0.53][Ga.sub.0.47]).sub.1-x]As alloy layers with embedded ErAs nanoparticles is presented. Thermal conductivities measured by TDTR at low modulation frequencies are in agreement with thermal conductivities measured by the 3[omega] method.

The thermoelectric properties of ErAs:InGaAlAs were characterized by variable-temperature measurements of thermal conductivity, electrical conductivity, and Seebeck coefficient from 300 K to 600 K, which shows that the ZT( $$=\alpha^{2}\sigma T/\kappa$$ , where $$\alpha, \sigma, \kappa,$$ and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively) of the material is greater than 1 at 600 K. Power generator modules of segmented elements of 300 μm Bi2Te3 and 50 μm thickness ErAs:(InGaAs)1− x (InAlAs) x were fabricated and characterized. The segmented element is 1 mm × 1 mm in area, and each segment can work at different temperature ranges. An output power up to 5.5 W and an open-circuit voltage over 10 V were measured. Theoretical calculations were carried out and the results indicate that the performance of the thermoelectric generator modules can be improved further by improving the thermoelectric properties of the element material, and reducing the electrical and thermal parasitic losses. [ABSTRACT FROM AUTHOR]

We report the fabrication and characterization of thermoelectric power generator modules of 16×16 segmented elements consisting of 0.8 mm thick Bi2Te3 and 50 μm thick ErAs:(InGaAs)1-x(InAlAs)x with 0.6% ErAs by volume. An output power up to 6.3 W was measured when the heat source temperature was at 610 K. The thermoelectric properties of (InGaAs)1-x(InAlAs)x were characterized from 300 up to 830 K. The finite element modeling shows that the performance of the generator modules can further be enhanced by improving the thermoelectric properties of the element materials, and reducing the electrical and thermal parasitic losses. [ABSTRACT FROM AUTHOR]

We report a wafer scale approach for the fabrication of 400 element power generator modules composed of 200 n-type ErAs:(InGaAs)0.8(InAlAs)0.2 and 200 p-type ErAs:InGaAs alloy thermoelectric elements. The thermoelectric properties of the materials were characterized. Two sets of generator modules with the element thicknesses of 20 and 10 μm, respectively, were fabricated. The 20 μm module had an output power density of 2.5 W/cm2 and 3.5 V open circuit voltages, and the 10 μm generator modules had an output power density of 1.12 W/cm2 and open circuit voltage of 2.1 V. The performance of thermoelectric generator modules can further be improved by increasing the thicknesses of the elements and reducing the electrical and thermal parasitic resistances. [ABSTRACT FROM AUTHOR]

We studied the cross-plane lattice and electronic thermal conductivities of superlattices made of InGaAlAs and InGaAs films, with the latter containing embedded ErAs nanoparticles (denoted as ErAs:InGaAs). Measurements of total thermal conductivity at four doping levels and a theoretical analysis were used to estimate the cross-plane electronic thermal conductivity of the superlattices. The results show that the lattice and electronic thermal conductivities have marginal dependence on doping levels. This suggests that there is lateral conservation of electronic momentum during thermionic emission in the superlattices, which limits the fraction of available electrons for thermionic emission, thereby affecting the performance of thermoelectric devices. [ABSTRACT FROM AUTHOR]