Search Results (3)

This study used modified manganese sand as an adsorbent to explore its adsorption effect on iron and manganese ions from groundwater. The effects of pH, manganese sand dosage, and the initial concentration of Fe/Mn on the removal rate of iron and manganese ions were studied through single-factor experiments. Based on the above three factors, a quadratic polynomial model between the adsorption rate and the above factors was established to determine the optimal adsorption conditions. The response surface analysis showed that pH had the most significant effect on the adsorption process. The optimum conditions for the adsorption of iron and manganese ions by modified manganese sand were pH = 7.20, the dosage of manganese sand = 3.54 g/L, and the initial concentration ratio of Fe/Mn = 3.80. The analysis of variance showed that the RSM model could accurately reflect the adsorption process of manganese sand. In addition, we confirmed that the relative error between model predictions and experimental values was close to 1%, proving that the response surface model was reliable. The kinetic data of the manganese sand were described well with the pseudo-second-order model. The isothermal adsorption of iron and manganese ions by modified manganese sand was fitted well using the Langmuir equation. Full article

Essential plant nutrients are needed at crop-specific concentrations to obtain optimal growth and yield. Foliar tissue analysis is the standard method for assessing nutrient levels in plants. Symptoms of nutrient deficiency or toxicity occur when the foliar tissue values become too low or high. Diagnostic nutrient deficiency criteria for Brassica rapa var. Chinensis (bok choy) is lacking in the current literature. In this study, green (‘Black Summer’) and purple (‘Red Pac’) bok choy plants were grown in silica sand culture, with control plants receiving a complete modified Hoagland’s all-nitrate solution, and nutrient-deficient plants induced by using a complete nutrient formula withholding a single nutrient. Tissue samples were collected at the first sign of visual disorder symptoms and analyzed for dry weight and nutrient concentrations of all plant essential elements. Six weeks into the experiment, the newest matured leaves were sampled for chlorophyll a, b, and total carotenoids concentrations for both cultivars, and total anthocyanin concentration in ‘Red Pac’. Compared to control plants, the dry weight of ‘Black Summer’ green bok choy was significantly lower for nitrogen (N), phosphorus (P), calcium (Ca), or boron (B) deficiency treatments, and nutrient concentrations were lower for all variables except iron (Fe) deficiency. Dry weight was less in ‘Red Pac’ plants grown without N, potassium (K), Ca, B, or molybdenum (Mo), and nutrient concentrations were lower for all except Mo-deficiency compared to controls. Total chlorophyll and total carotenoid concentrations were lower in leaves from N−, Fe-, and manganese- (Mn) deficient plants of both cultivars. Leaf anthocyanin concentration was lower only for K-, Ca-, and B-deficiencies in ‘Red Pac’. Our results indicate that visual symptoms of nutrient deficiency are well correlated with nutrient disorders. In contrast, changes in dry weight, chlorophyll, and anthocyanin did not show consistent changes across nutrient disorders. Full article

The intrinsic kinetics of biogas methanation coupling with water gas shift over Re-promoted Ni bifunctional catalysts were investigated in this study. The catalysts were prepared through co-impregnation of Ni and Re precursors on the H₂O₂-modified manganese sand. The experiments were performed in a fixed bed reactor under the assorted reaction conditions of 300–400 °C, 0.1–0.3 MPa, and a 0.6–1.0 H₂/CO ratio. The effect of gas internal and external diffusion on the performance of methanation coupling with water gas shift was examined by changing catalyst particle size and gas hourly space velocity (GHSV) and further verified by the Weisz–Prater and Mears criterion, respectively. It was found that the internal and external diffusions were eliminated when the catalyst particle size was 12–14 meshes and GHSV was 2000 h⁻¹. Three kinetics models including the empirical model (EM), synergetic model (SM), and independent model (IM) were proposed, and 25 sets of experimental data were obtained to solve the model parameters. By mathematical fitting and analysis, it was discovered that the fitting situation of the three kinetics models was in the order of EM > SM > IM, among which EM had the highest fitting degree of 99.7% for CH₄ and 99.9% for CO₂ with the lowest average relative error of 8.9% for CH₄ and 8.7% for CO₂. The over 30% of average relative error for CO₂ in IM might exclude the possibility of the Langmuir–Hinshelwood water gas shift mechanism in the real steps of biogas methanation coupling with water gas shift over Re-promoted Ni catalysts. Full article