ABSTRACT
In recent two decades, ultrasound has been broadly applied to the hydrometallurgical leaching process to recover valuable metals within raw materials, aiming to solve the shortcomings of the conventional leaching process, including relatively low leaching recovery, long leaching duration, high reagent usage, high energy consumption and so on. The present work focuses on a comprehensive overview of the ultrasound-enhanced leaching of various metals, such as common nonferrous and ferrous metals, rare metals, rare earth elements, and precious metals, from raw metal ores and secondary resources. Moreover, the enhanced leaching mechanisms by ultrasound are discussed in detail and summarized based on the improvement of leaching kinetics, enhancement of the mass transfer and diffusion of lixiviants, and promotion of the oxidative conversion of metals from insoluble to soluble states. Lastly, the challenges and outlooks of future research on the leaching recovery for valuable metals with the assistance of ultrasound irradiation are proposed.
ABSTRACT
Zn and Ge were selectively extracted from zinc oxide dust (ZOD) by the ultrasonic-H2O2 (UH) combined oxidation-leaching process. In the leaching process, the effects of the dosage of H2O2 (6-29.5 mL), ultrasonic power, initial acidity (100-200 g L-1), liquid/solid mass ratio (4-8 : 1), leaching temperature (50-90 °C), and leaching time (30-240 min) on the leaching rates of Zn and Ge were studied. The experimental results showed that the ultrasonic power and the dosage of H2O2 have the greatest influence on the leaching rates of Zn and Ge. The results showed the optimum conditions as: ultrasonic power 200 W, the dosage of H2O2 14.8 mL, initial acidity 160 g L-1, liquid/solid mass ratio 7 : 1, leaching time 60 min, stirring speed 400 rpm, leaching temperature 60 °C, and the leaching rate of Zn and Ge reaches 99.61% and 88.29%, respectively. The leaching rates of Zn and Ge by UH were 7.86% and 5.65% higher than that by conventional leaching (CL), respectively. The experimental results showed that UH leaching technology can improve the rates of Zn and Ge from ZOD, reduce the leaching temperature, save the production cost, solve the problem of low leaching rates of Zn and Ge in ZOD treatment technology, and realize the resource, reduction and harmless treatment of ZOD.
ABSTRACT
Single-motorcycle crashes are overrepresented on horizontally curved segments of rural, two-lane, undivided (RTU) highways. However, the relationship between single-motorcycle crash risk and the design features of horizontal curves on RTU highways is not well-studied in existing literature. This study aims to quantify the effect of horizontal curve type and radius on the risk of single-motorcycle crashes with a matched case-control study that can address the issues of the low sample mean, aggregation bias, and uncontrolled confounders existing in the traditional cross-sectional study. In the matched case-control study, three matching factors-year, annual average daily traffic (AADT), and segment length-were selected to match controls (RTU segments without crash records) with cases (RTU segments with crash records). A total of 1601 cases and 16,010 matched controls over 11 years (2005-2015) were identified as matched-strata. A conditional logistic model was fitted on the matched-strata data to estimate the crash modification factors (CMFs) of horizontal curve design features for single-motorcycle crashes. The modeling results highlighted the interaction effects between curve type and radius on the risk of single-motorcycle crashes. Sharp (radius ≤ 1500 ft) non-reverse curves were identified as the riskiest curve design for motorcyclists, followed by sharp reverse curves and moderate (1500 ft < radius ≤ 3000 ft) reverse curves. The study also revealed that motorcyclists might take safety-compensation behaviors on sharp curves, narrow shoulders, and poor pavement conditions. Engineering and education countermeasures are suggested for comprehending curve presence and associated risk level, reducing curve entry speed, and improving safety awareness. Finally, the limitations of the study and possible solutions are discussed.
