A Novel Experimental Apparatus for Characterizing Flow Regime in Mechanically Stirred Tanks through Force Sensors.

Pressure fluctuations in a mixing tank can provide valuable information about the existing flow regime within the tank, which in turn influences the degree of mixing that can be achieved. In the present work, we propose a prototype for identifying the flow regime in mechanically stirred tanks equipped with four vertical baffles through the characterization of pressure fluctuations. Our innovative proposal is based on force sensors strategically placed in the baffles of the mixing tank. The signals coming from the sensors are transmitted to an electronic module based on an Arduino UNO development board. In the electronic module, the pressure signals are conditioned, amplified and sent via Bluetooth to a computer. In the computer, the signals can be plotted or stored in an Excel file. In addition, the proposed system includes a moving average filtering and a hierarchical bottom-up clustering analysis that can determine the real-time flow regime (i.e., the Reynolds number, Re) in which the tank was operated during the mixing process. Finally, to demonstrate the versatility of the proposed prototype, experiments were conducted to identify the Reynolds number for different flow regimes (static, laminar, transition and turbulent), i.e., 0≤Re≤ 42,955. Obtained results were in agreement with the prevailing consensus on the onset and developed from different flow regimes in mechanically stirred tanks.

Indium and tin recovery from waste LCD panels using citrate as a complexing agent.

In this work, an environmentally-friendly leaching process for the recovery of indium (In) and tin (Sn) from LCD panel waste was investigated. Easily degradable citrates (C6H5O73-), i.e., sodium citrate and citric acid, were used as complexing agents. The morphology and composition of the species present in the LCD powder before and after the leaching processes were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The concentrations of In, Sn, and iron (Fe) present in the leachate were determined by atomic absorption spectrometry (AAS). The necessary thermodynamic conditions for achieving substantial In recovery were established by using MEDUSA software. The optimal process conditions were determined experimentally by varying the initial citrate concentration as well as by using reducing or oxidizing media, respectively hydrazine (N2H4) or hydrogen peroxide (H2O2). It was found that using N2H4 in a citrate solution as a reducing agent enhances the leaching efficiency. However, high concentrations of Sn and Fe with respect to In were found in the LCD powder. Therefore, a pretreatment processes to first remove the excess of Sn and Fe, which compete with In for the citrate, was implemented. Leaching with 1 M citrate, 0.2 M N2H4, at pH = 5, using sodium hydroxide (NaOH) at solid:liquid (S:L) ratio of 20 g∙L-1, yielded a remarkably high In recovery of 98.9% after 16.6 h.