Hydrothermal carbon (HTC) was prepared by the one-step hydrothermal method for Cr (VI) removal from wastewater, which was considered a “green chemistry” method. The specific surface area (SBET) of HTC was 85 m2/g with the pore size in range of 2.0–24.0 nm. FT-IR spectra analysis showed that the HTC had abundant chemical surface functional groups. The influence of adsorption parameters such as pH, HTC dosage, Cr (VI) concentration, and contact time on the removal efficiency of Cr (VI) had been investigated. When the initial concentration was 50 mg/L, pH = 6, amount of adsorbent was 0.2 g/50 ml, and adsorption time was 90 min; the Cr (VI) absorbed rate of HTC reached 98%. Batch adsorption experiments indicated that Cr (VI) adsorption data of HTC fitted the Freundlich isothermal and pseudo-second-order kinetic models. Overall, our findings provide a promising material in treatment of Cr (VI)-rich wastewater and give a clear picture of its application, which is worthy of further study.

The introduction of air into a submerged annular jet will result in dispersion of the jet, which will affect the degree of enclosure of the gas–water mixing zone in the annular jet nozzle, and then have a significant impact on air suction and the formation of the foam system in the floatation process. A numerical simulation method is used to analyze the characteristics of the distribution of the axial flow velocity of annular jets, gas–phase volume, and turbulence intensity in the gas–water mixing zone in the nozzle with different air–liquid ratios, and thereby reveal the mechanism whereby gas–containing in annular jets affects the degree of enclosure of the gas–water mixing zone. The results show that as the air–liquid ratio increases, the degree of air–liquid mixing will increase and the radial flow velocity will decrease gradually, resulting in the effective enclosure of the gas–water mixing zone. Meanwhile, the dissipation of jet energy, the range of turbulent flow and the vorticity intensity will increase, but the turbulence intensity will decrease. When the gas–water mixing zone is fully enclosed, as gas–containing continues to increase, the degree of dispersion of the annular jet will further increase. Consequently, the area of the gas–water mixing zone with bounced–back water will become larger, resulting in a higher axial flow velocity, larger local turbulence intensity and larger vorticity intensity. This will lead to the dissipation of jet energy, which is not favorable for air suction.

Liquid concentration detection systems have been widely used in food, chemical, pharmaceutical, and many other industries. When the liquid flows, a large number of vortices will usually be generated, resulting in increased turbulence intensity, which will interfere with the detection of the concentration of the suspension. In this paper, a method for concentration detection by differential pressure based on turbulence elimination is proposed to improve the reliability of concentration detection results. The changes in the internal flow field corresponding to different lengths of the turbulence elimination structure and different inlet angles are analyzed through numerical simulation. Finally, the influence of changes in structure parameters on the accuracy of concentration detection is tested through experiments. The results show that when the length of the turbulence elimination structure is small, the vortex zone inside the concentration detection device changes with the inlet velocity. When the length of the turbulence elimination structure is 150 mm, the vortex zone is basically not affected by the inlet velocity. The stability of the flow field increases with the increase in the inlet angle. When the inlet angle increases to 60°, a stable zone of turbulence will form in the region where Y > 0.4 m. When the length of the turbulence elimination structure is 150 mm and the inlet angle is 60°, the expected experimental results are obtained, and the actual needs of liquid concentration measurement are met.