Silver Adsorption on the Low Temperature Activated Alumina Grades. I. Adsorption Capacity and Kinetics

Abstract

Aluminum hydroxide is a key product for the industrial production of alumiana and aluminium, ceramics insulator and refractories, desiccants, absorbents, flame retardants, filers for plastics and rubbers, catalysts, and various construction materials. The production of these arrays of useful material products is grounded on the multiple thermal decomposition pathways of Al(OH)3, which involve major crystallographic dislocations and many microstructure reconfigurations on variable lines of phase transitions, from the raw material up to large varieties of precursors and commercial grade products. A wide range of literature on this subject is available, and recent reviews cover suitable information about preparation and characterization of different activated alumina products with specific properties and applications. In our previous papers, there was studied the mechanisms of aluminum hydroxide phase transitions, during low temperature calcination, namely, at 260ºC, 300ºC, 400ºC and 600 ºC, under chosen particularly conditions, for promoting the nucleation of the amorphous phases. Collected data suggest that raw aluminum hydroxide; dried, milled and classified is a precursor for the new low temperature activated alumina transition phases, carrying distinctive characteristics and properties, due to products enrichment in amorphous phases. Accordingly, as effects of the main driving factors (temperature and rate of heating, and initial particle size dimension) on the aluminum hydroxide as new precursor, notable changes were observed in products mineral composition, morphology and specific surface area, pore size, pore distribution, and the particle size distribution. Beside, some other secondary effects have to be apprehended. For example, the main phase transition process dinamic factors control over some physical and technical properties of the new products, like: absolute density, brightness, oil absorption capacity and water absorption capacity. The purpose of this work was to continue the characterization of low temperature activation alumina products, and also, to measure the adsorption capacity and to reveal adsorption kinetics mechanisms. Thus, the first step of survey was silver adsorption maximum capacity measurements for all sample prepared by heating the precursor alumina hydroxide, milled and classified as 5 different dimension size fractions to 260, 300, 400 and 600ºC. Hereinafter, four samples, carefully selected as representative for the entire lot of samples, were used for the study of kinetics mechanism and data fitting to the adequate kinetic equations. Confident data validate the pseudo second order kinetic model for the entire activation process, independently of samples heating temperature and particles dimension.

Scandium Recovery from Aqueous Solution by Adsorption Processes in Low-Temperature-Activated Alumina Products

“…From these data, it can be observed that as the initial Sc(III) concentration increases, the adsorption capacity of the GDAH-04-300 material also increases, reaching equilibrium at 80 mg/L Sc(III), when the maximum adsorption capacity is ~9.4 mg Sc(III)/g material. From a previous study, this value is comparable to that obtained in the case of silver adsorption (10.2 mg Ag(I)/g), which suggests that the GDAH-04-300 material behaves in a similar way [ 60 ]. The specific parameters of each isotherm used to model the experimental data were calculated from the straight-line slopes using the y-intercept ordinate ( Table 5 ).…”

“…Sample GDAH-04-300 (fraction 0–10 µm), highlighted for the increased thermal stability and good adsorption capacity of the low-temperature-activated alumina products, was selected as a working model for all measurements included in previous papers concerning adsorption [ 60 ]. Actually, the absorption capacities of these samples represent the maximum capacities for all the low-temperature-activated alumina products saturated with Sc(III) from a Sc(III) solution with a concentration of 10 mg/L at 298 K. Moreover, the higher adsorbent capacity, assumed for samples GDAH-03-300 and GDAH-04-300, is a direct effect of both mechanical activation (milling and classification) and thermal activation as driving factors in the conversion process of the aluminium hydroxide into low-temperature-activated alumina products [ 54 , 58 , 59 , 60 , 64 , 65 ].…”

“…The dependence is so evident that the data for samples GDAH-03 (under 20 µm) and GDAH-04 (under 10 µm) are completely different from the same parameters for samples GDAH-01 and GDAH-02. The particular properties of these low-temperature-activated alumina products have been studied in our previous papers [ 54 , 58 , 59 , 60 , 65 ]. Therefore, all the scandium adsorption data can be analysed on the basis of rigorous knowledge about the sample mineralogy and chemistry, as well as about all other sample properties.…”

“…In other instances, the measurements consist of mixing for 60 min at 298 K, appropriate quantities of any of the alumina product samples from Table 6 in 25 mL Sc(III) solution of 10 mg/L concentration (standard Sc(NO 3 ) 3 , Merck). Finally, the residual concentration of Sc(III) was measured by the ICP-MS (PlasmaQuant 9100 Analytic Jena – Analytik Jena GmBH, Jena, Germany) method and the computations were made with the formula given in our previous paper [ 60 ]. This method has been used in several variants throughout this paper.…”

“…The precursor of the low-temperature-activated alumina product is the aluminium hydroxide dried, milled and classified, and manufactured at Vimetco Alum SA Tulcea, Romania, after the implementation of the project “Endow the Research and Development Department of SC ALUM SA Tulcea with independent, efficient research facilities to support the economic competitiveness and business development”, a project co-funded by the European Regional Development Fund through the Competitiveness Operational Program 2014–2020. The samples of low-temperature-activated alumina products used in this paper are from the same batch as the ones used in our last paper [ 60 ]. The goals are similar in both studies, to determine the maximum adsorption capacity of low-temperature-activated alumina products, to identify the best adsorbent performances and to evaluate correlations between adsorbent properties and adsorbent performances.…”