Nitrogen Application Practices to Reduce Cd Concentration in Rice (Oryza Sativa L.) Grains

Cd pollution in paddy soils creates challenges in rice grain production, thereby threatening food security. The effectiveness of different base-tillering-panicle urea application ratio and the combined basal application of urea and Chinese milk vetch (CMV, Astragalus sinicus L.) in minimizing Cd accumulation in rice grains was explored in a Cd-contaminated acidic soil via a field experiment. The results indicated that under similar N application rates, an appropriate amount of urea applied at the panicle stage or the combined basal application of urea and CMV decreased Cd absorption by rice roots and its accumulation in rice grains, as compared with that of conventional N application (control). Furthermore, under a 3:4:3 base-tillering-panicle urea application ratio or for basal application of CMV at high levels, Cd concentrations in brown rice were significantly lower (40.7% and 34.1%, respectively) than that of control. Cd transport coefficient from root to straw was significantly higher than that of control when an appropriate amount of urea was applied at the panicle stage or urea and CMV were applied basally, whereas the Cd transport coefficient from straw to brown rice was relatively lower. Moreover, soil pH, or the concentrations of CEC and CaCl2-Cd under different N fertilizer treatment was not significantly different. However, rice grain yield increased by 29.4% with basal application of a high amount of CMV compared with that of control. An appropriate amount of urea applied at the panicle stage or the combined basal application of urea and CMV decreased Cd absorption by rice roots and inhibited its transport from straw to brown rice, thus reducing Cd concentration in brown rice. Therefore, combined with the key phase of Cd accumulation in rice, a reasonable urea application ratio or a basal application of high amounts of CMV can effectively reduce Cd concentration in brown rice.

Evaluation and Modeling of Asphaltene Deposition in Oil Wells

Asphaltene deposition in oil wells is a challenging flow-assurance phenomenon that affects the well production, project economics, and operational safety. While asphaltene precipitation is governed by the hydrocarbon mixture thermodynamics, Asphaltene deposition is governed by the complexity of flow hydrodynamic behavior and characteristics. This study aims to evaluate and compare the performance of the existing asphaltene deposition models and improve the current theoretical understanding of the deposition phenomenon by developing better predictive asphaltene deposition model. A large experimental database is collected, including aerosol and asphaltene particles deposition in air and crude oil systems, respectively, to carry on the evaluation. The results of this study revealed that Kor and Kharrat (2017) model of transport coefficient, which accounts for both diffusional and inertial deposition mechanisms outperformed other models in matching the transport coefficient from aerosol/air data. In addition, an improved sticking probability model is proposed in this study, and curve fitted using corrected deposition flux data to obtain the model constant. The improved model is not only physically sound, i.e. SP≥1, but also it requires less input data than other models. A validation study of the improved model shows a slight over prediction of experimental data with an absolute average error of 6.8% and standard deviation of 11.4%. The significance of this work is to provide theoretical predictive tool for asphaltene deposition in pipes to enable prevention, mitigation, and management of oil field asphaltene deposition strategies.

Aluminium Recycling in Single- and Multiple-Capillary Laboratory Electrolysis Cells

This work is a contribution to the approach for Al purification and extraction from scrap using the thin-layer multiple-capillary molten salt electrochemical system. The single- and multiple-capillary cells were designed and used to study the kinetics of aluminium reduction in LiF–AlF3 and equimolar NaCl–KCl with 10 wt.% AlF3 addition at 720–850 °C. The cathodic process on the vertical liquid aluminium electrode in NaCl–KCl (+10 wt.% AlF3) in the 2.5 mm length capillary had mixed kinetics with signs of both diffusion and chemical reaction control. The apparent mass transport coefficient changed from 5.6∙10−3 cm.s−1 to 13.1∙10−3 cm.s−1 in the mentioned temperature range. The dependence between the mass transport coefficient and temperature follows an Arrhenius-type behaviour with an activation energy equal to 60.5 J.mol−1. In the multiple-capillary laboratory electrolysis cell, galvanostatic electrolysis in a 64LiF–36AlF3 melt showed that the electrochemical refinery can be performed at a current density of 1 A.cm−2 or higher with a total voltage drop of around 2.0 V and specific energy consumption of about 6–7 kW.kg−1. The resistance fluctuated between 0.9 and 1.4 Ω during the electrolysis depending on the current density. Thin-layer aluminium recycling and refinery seems to be a promising approach capable of producing high-purity aluminium with low specific energy consumption.