This study analyzed the influence of different ammonia stripping parameters on ammonia removal efficiency and mass transfer rate. Ammonia stripping was performed on two devices, a column and a packed tower, with artificial ammonium hydroxide wastewater. First, ammonia concentration and pH were varied in a column without liquid circulation. At the same pH, the removal efficiency and mass transfer rate were constant, irrespective of initial ammonia concentration. When pH was increased, the ammonia fraction also increased, resulting in higher removal efficiency and mass transfer rate. Second, the effects of stripping were assessed using a packed tower with fluid circulation. The ammonium hydroxide concentration did not affect the removal efficiency or mass transfer rate. Furthermore, at apparatus liquid-gas ratios of 26.8–107.2 L/m³, a lower liquid-gas ratio led to increased ammonia removal efficiency and mass transfer rate. Conversely, the lower the liquid-gas ratio, the greater the air consumption. In conclusion, considering the removal rate and volume of air supply, the range of optimal liquid-gas ratio was determined as 26.8–53.6 L/m³. In particular, the 26.8 L/m³ condition achieved the best ammonia removal rate of 63.0% through only 6 h of stripping at 70 °C and pH 8.5.

The characteristics of hydrothermal carbonization hydrochar derived from cattle manure including excrements and lignocellulosic biomass were analyzed. The effects of hydrothermal carbonization were evaluated by varying the reaction temperatures in the range of 180~240 °C. The hydrochars were evaluated with respect to their usefulness as renewable fuels via physicochemical analysis and pyrolysis processes. As reaction temperatures increased, the fractions of fixed carbon in proximate analyses, carbon elements in ultimate analyses, and higher heating values of hydrothermally carbonized biochars increased in correlation with the primary reactions of coalification. Various correlations were derived with the characteristics of hydrochars in order to be utilized for operating and designing HTC reactors for cattle manure. The correlation between the O/C and H/C ratios was deduced on the basis of a van Krevelen diagram. The interaction equation was represented with the increased fraction of HHV compared to the reaction temperature of hydrothermal carbonization. The ultimate correlation for the estimation of higher heating values was suggested for HTC hydrochars. Moreover, the pyrolysis characteristics and kinetic parameters of the cattle manure and hydrochar were deduced by utilizing a multi-step kinetic model scheme. As the HTC reaction temperature increased, the global activation energy and the pre-exponential factors of hydrochars decreased in the low-temperature section and increased in the high-temperature section.

The influence of adsorbate (D2EPHA and kerosene) on the process of zinc electrowinning from sulfuric acid electrolytes was analyzed. The main objective was to critically compare three factors: (1) Three types of activated carbon (AC); (2) adsorption temperatures and contact time; and (3) zinc recovery efficiency. The results showed that organic components reduced the efficiency of zinc recovery. Moreover, wood-based ACs had a higher adsorption capacity than coal- and coconut-based ACs. To maintain a removal efficiency of 99% or more, wood-based ACs should constitute at least 60% of the adsorbate. The temperature of adsorption did not affect the removal efficiency. Additionally, the feeding rate of adsorbate in the solvent was inversely proportional to the removal efficiency. A feeding rate of the liquid pump of over 3 mL/min rapidly increased the delta pressure. For the same contact time, 99% of adsorbate removal occurred at 1 mL/min compared to approximately 97% at 0.5 mL/min. In the presence of 100 mg/L zinc, with increasing adsorbate from 0–5%, the recovery efficiency of zinc decreased from 100% to 0% and the energy consumption increased from 0.0017–0.003 kwh/kg zinc. Considering the energy consumption and zinc deposit mass, 0.1% of the adsorbate is recommended for zinc electrowinning.

This study compared the electrolytic refining process using different commercial Pd-based electrodes. The Pd-based electrode had an Ir:Sn molar ratio of 1:1 and contained 10% tantalum on a titanium substrate. The palladium weight ratio varied from 0 g to 1.8 g, 4.7 g, 8.6 g, and 15.4 g. Electrolytic refining was investigated for the Pd-based electrode in 3 M of H₂SO₄. The interfacial microstructure and components of the substrate were investigated using energy-dispersive X-ray analysis, and the electrochemical properties of the materials were measured using cyclic voltammetry, linear scan voltammetry, electrochemical impedance spectroscopy, and accelerated life tests. Of all the tested Pd-based electrodes, those with a palladium loading weight of 8.6 g showed the highest and most stable electrode activity at 3 M of H₂SO₄, with a capacitance retention of 96% of its initial value. The accelerated life test results for the 8.6 g Pd-Ir-Sn-Ta/TiO₂ electrode showed a gradual slope with an efficiency of almost 100% at 1000 h in an aqueous solution of 3 M of H₂SO₄. After the test, the dissolved elements that caused resistance in the electrolyte increased with increasing palladium loading content. Thus, the 8.6 g Pd-Ir-Sn-Ta/TiO₂ electrode demonstrated the optimum composition in 3 M of H₂SO₄ for electrolyte refining.

Electrowinning is a technique that can be used to obtain high-purity elements through electrolysis. The degradation of accelerated life testing for Pd-based electrodes is discussed in this study. The lifetime of the electrodes was examined by multiplying the acceleration rate with the current to measure the voltage of the electrodes. The acceleration rate was set to 10, 20, and 30 times. Four components were deposited on the TiO₂ plate. The ratio of Ir to Sn was fixed at 1:1, while Ta was deposited at 10 wt.%. Pd was deposited at 2, 4, 8 and 10 wt.% to create Pd-Ir/Sn-Ta. The initial voltage decreased as the Pd deposition amount increased irrespective of the acceleration rate. The lower the acceleration rate, the lower the voltage. An increase in the Pd content caused the initial voltage to be low. The multiple of the acceleration rate slightly increased for all cases of life testing for one year. When the test was conducted by increasing the current density by 20 times, the increase in voltage was proportional to the Pd deposition amount. However, for the 30 times acceleration rate, the lifetime of the electrodes was shortened as the Pd content increased. It can be inferred that the content of Pd and the ratio of Ir to Sn can influence the lifetime of the electrodes. According to these results, if the multiple of the acceleration rate is too extreme, the lifetime of the electrodes cannot be evaluated because they are damaged in an extreme situation.

In this study, an alumina (Al) anode, a lead cathode, and insoluble catalytic cathodes (IrOx, PdOx, TaOx, and SnOx) were used as electrodes to enhance zinc recovery. The traditionally used iron electrode and insoluble catalytic electrodes were also used to compare the recovery yield when different types of electrodes were subjected to the same amount of energy. The lead electrode showed over 5000 Ω higher electrode resistance than did the insoluble catalytic electrode, leading to overpotential requiring higher electrical energy. As electrical energy used by the lead and the insoluble catalytic electrodes were 2498.97 and 2262.37 kwh/ton-Zn, respectively, electrical energy can be reduced by 10% when using an insoluble catalytic electrode compared to that when using a lead electrode. Using recovery time (1–4 h) and current density (100–500 A/m²) as variables, the activation, concentration polarization, and electrode resistance were measured for each condition to find the optimum condition for zinc recovery. A recovery yield of about 77% was obtained for up to 3 h of zinc recovery time at a current density of 200 A/m², which is lower than that (about 80%) obtained at 300 A/m². After 3 h of recovery time, electrode resistance (Zn concentration reduction, hydrogen generation on electrode surface) and overpotential increase with time decreased at a current density of 200 A/m², leading to a significant increase in zinc recovery yield (95%).