Coagulated Mineral Adsorbents for Dye Removal, and Their Process Intensification Using an Agitated Tubular Reactor (ATR)

Abstract

The aim of this study was to understand the efficacy of widely available minerals as dual-function adsorbers and weighter materials, for the removal of toxic azo-type textile dyes when combined with coprecipitation processes. Specifically, the adsorption of an anionic direct dye was measured on various mineral types with and without the secondary coagulation of iron hydroxide (‘FeOOH’) in both a bench-scale stirred tank, as well as an innovative agitated tubular reactor (ATR). Talc, calcite and modified bentonite were all able to remove 90–95% of the dye at 100 and 200 ppm concentrations, where the kinetics were fitted to a pseudo second-order rate model and adsorption was rapid (<30 min). Physical characterisation of the composite mineral-FeOOH sludges was also completed through particle size and sedimentation measurements, as well as elemental scanning electron microscopy to determine the homogeneity of the minerals in the coagulated structure. Removal of >99% of the dye was achieved for all the coagulated systems, where additionally, they produced significantly enhanced settling rates and bed compression. The greatest settling rate (9 mm min−1) and solids content increase (450% w/w) were observed for the calcium carbonate system, which also displayed the most homogenous distribution. This system was selected for scale-up and benchmarking in the ATR. Dye removal and sediment dispersion in the ATR were enhanced with respect to the bench scale tests, although lower settling rates were observed due to the relatively high shear rate of the agitator. Overall, results highlight the applicability of these cost-effective minerals as both dye adsorbers and sludge separation modifiers to accelerate settling and compression in textile water treatment. Additionally, the work indicates the suitability of the ATR as a flexible, modular alternative to traditional stirred tank reactors.

Analysis of Adsorbed Polyphosphate Changes on Milled Titanium Dioxide, Using Low-Field Relaxation NMR and Photoelectron Spectroscopy

“…The samples were then left on a roller shaker (IKA, U.K.) for 12 h, after which the pH was checked once again, where it is believed that 12 h is far in excess of the time required for equilibrium adsorption to occur. Previous work by Taylor et al on similar doped TiO 2 and SHMP systems, indicated equilibrium was reached in tens of minutes, which would be consistent with other electrostatic-driven adsorption of large molecules on mineral systems …”

“…Previous work by Taylor et al 43 on similar doped TiO 2 and SHMP systems, indicated equilibrium was reached in tens of minutes, which would be consistent with other electrostatic-driven adsorption of large molecules on mineral systems. 44 …”

“…Previous work by Taylor et al 43 on similar doped TiO 2 and SHMP systems, indicated equilibrium was reached in tens of minutes, which would be consistent with other electrostatic-driven adsorption of large molecules on mineral systems. 44 After adsorption, samples were centrifuged on a Heraeus Megafuge 16R (Thermo Scientific) at 10,000 rpm for 30 min, whereupon the supernatant was extracted and passed through a 0.22 μm syringe filter to remove any particles that remained. The supernatant was analyzed via ICP-OES (iCAP7600, Thermo Scientific, U.K.) with a five-point calibration made using SHMP solutions at pH 4 and 10 mM NaCl.…”

Process intensification of dendritic fibrous nanospheres of silica (DFNS) via continuous flow: a scalable and sustainable alternative to the conventional batch synthesis

“…61 The ATR is a commercially successful reactor in industries known to handle solid slurries and suspensions in addition to gas-liquid and solid-liquid-gas processes. [62][63][64][65][66][67] The unique tube-and-agitator design 68,69 has been proven to effectively circumvent pressure drops when connecting two or more reactors in series, thus enabling kilo-scale production with high throughput. Owing to these advantages, we decided to employ this scale-up tool for demonstrating the telescoped flow synthesis for the high-throughput production of DFNS.…”

Sequential Approach for Water Purification Using Seashell-Derived Calcium Oxide through Disinfection and Flocculation with Polyphosphate for Chemical Pollutant Removal

“…The only available water can be surface water from the river, lake, or pond that contains chemical pollutants and harmful microorganisms. Chemical pollutants can be removed by flocculation, the use of adsorbents (e.g., activated carbon), and filtration. − Moreover, water disinfection is achieved by heating, filtration, and the use of disinfectants, such as hypochlorite and iodine. ,− The use of disinfectants has some advantages, including the ease of application to large or small quantities of water and no requirement for electricity or fuel sources. Nevertheless, appropriate control over the concentration of the disinfectants is required.…”