Rice Husk Cellulose-Based Adsorbent to Extract Rare Metals: Preparing and Properties

Abstract

Adsorption is one of the common stages in the hydrometallurgy of rare metals. Its efficiency is largely determined by the quality of the sorbent used. The purpose of this work was to create an activated sorbent based on rice husk cellulose for the extraction of rhenium from aqueous solutions. Two types of cellulose were obtained by treating rice husk with a 1.5% NaOH solution (alkaline cellulose) and a nitric acid solution in ethyl alcohol (Kürschner and Hoffer cellulose). They were tested by IR, SEM, TA, TPD-MS, and XRD methods. It was found that Kürschner and Hoffer cellulose does not contain lignin and retains structural order to a greater extent. By means of this cellulose carbonization at 600 °C and activation by physical, chemical, and combined methods, a series of sorbents were prepared and studied by different methods. It was determined that the sorbent KHC4-600VA obtained by combined activation of cellulose carbonizate by water vapor at 850 °C, followed by an alkaline treatment, has the best textural characteristics: S—~1200 m2·g−1, V—1.22 cm3·g−1, and R—2.05 nm. KHC4-600VA provides 90% recovery of Re (VII) ions from aqueous solutions. According to the Freundlich model, sorption proceeds favorably on the sorbent’s heterogeneous surface.

Rice Husk-Based Adsorbents for Removal of Metals from Aqueous Solutions

“…The percentage of Re (VII) removal was higher for 60 min (96%) compared with 30 min (84%), and it dropped more significantly (from 84% to 32%) in the 30 min process when the initial concentration of Re (VII) increased [71]. Based on the Giles isotherm classification [75], Kablanbekov et al [71] classified the isotherm of Re (VII) removal for 60 min as the C curve considering that the number of sites on the KHC4-600VA surface for Re (VII) adsorption remained constant at all concentrations up to saturation. The Re (VII) adsorption process onto KHC4-600VA was described the best by the Freundlich equation, while in the case of SCActA, it fit well with the Langmuir isotherm model (Table S16).…”

“…Moreover, the materials treated with alkali showed the highest sorption properties in comparison to rice husk modified with acids. Although C-O-Si bonds were present in rice husk after alkali treatment, silicon removal was achieved almost completely [71]. It can be suggested that as a result, new active sites form.…”

“…Activated rice-husk-based biochars were tested to remove Re (VII) ions from single solutions at pH~6 in batch experiments for different periods of time [71] (Table S16). The adsorption equilibrium was reached fast enough (in 30 min) and the percentage of Re (VII) extraction was high (~90%).…”

“…The adsorption equilibrium was reached fast enough (in 30 min) and the percentage of Re (VII) extraction was high (~90%). The initial concentration of the metal solution increased (20-100 mg•dm −3 ), and the maximum adsorption capacity value of Re (VII), depending on the adsorbent-adsorptive contact time (30-60 min), trebled, reaching at least 8.8 mg•g −1 [71]. The percentage of Re (VII) removal was higher for 60 min (96%) compared with 30 min (84%), and it dropped more significantly (from 84% to 32%) in the 30 min process when the initial concentration of Re (VII) increased [71].…”

“…The initial concentration of the metal solution increased (20-100 mg•dm −3 ), and the maximum adsorption capacity value of Re (VII), depending on the adsorbent-adsorptive contact time (30-60 min), trebled, reaching at least 8.8 mg•g −1 [71]. The percentage of Re (VII) removal was higher for 60 min (96%) compared with 30 min (84%), and it dropped more significantly (from 84% to 32%) in the 30 min process when the initial concentration of Re (VII) increased [71]. Based on the Giles isotherm classification [75], Kablanbekov et al [71] classified the isotherm of Re (VII) removal for 60 min as the C curve considering that the number of sites on the KHC4-600VA surface for Re (VII) adsorption remained constant at all concentrations up to saturation.…”