The removal of harmful arsenic(V) from aqueous solutions using Cyanex 923 (solvation extractant) was investigated under various experimental variables: equilibration time, acidity of the aqueous phase, temperature, extractant and arsenic concentrations, and O/A ratio. Cyanex 923 extracted As(V) (and sulphuric acid) from acidic solutions, thus, its use to remove the metal from slightly acid or neutral solutions it is not possible. Extraction of arsenic is exothermic, and responded to the formation of H3AsO4·nL species in the organic phase (L represented the extractant and the stoichiometric factor n: 1 or 2, depends on the acidity of the aqueous phase). Extraction isotherms are derived from experimental results. Both arsenic and sulphuric acid loaded onto the organic phase can be stripped with water, and stripping isotherms are also derived from the experimental results. The selectivity of the system against the presence of other metals (Cu(II), Ni(II), Bi(III), Sb(III)) are investigated, and also it is investigated the ability of Cyanex 923 to extract As(V) and sulphuric acid against the use of other P=O based solvation reagents, such dibutyl butylphosphonate (DBBP) and tri-butyl phosphate (TBP).

Since the 1960s Rare earths (REs) applications gradually have expanded to everyday life. REs have great strategic importance in industrial and technological development, so it is expected an increase in their demand. Among the REs the European Commission considered Cerium and Lanthanum as critical raw materials. This research article studies the adsorption of Ce and La onto two carbon nanomaterials, multiwalled carbon nanotubes (MWCNT) and carboxylic functionalized multiwalled carbon nanotubes (MWCNT_ox). The latter has slightly more affinity for REs than MWCNT. The recovery percentage for Ce were 89 and 98% and in the case of for La were 99 and 92% using 0.8 g of MWCNT and 0.2 g of MWCNT_ox respectively. The adsorption process fits a pseudo second-order kinetic model and the Langmuir isotherm best represented the metal uptake.

Commercially available oxidized (carboxylic groups) and non-oxidized multiwalled carbon nanotubes were studied as adsorbents of cerium(III) in batch operation mode. Several variables affecting the rare earth adsorption were investigated, including: the stirring speed applied to the system, the pH of the solution and the metal concentration and carbon dosages. Although the removal of cerium from the solution is different and dependent upon the adsorbent type: i) adsorption in non-oxidized multiwalled carbon nanotubes, ii) cation exchange in the case of using oxidized multiwalled carbon nanotubes, the adsorption kinetics, the rate law and the isotherm models are the same for both adsorbents: pseudo-second order, film diffusion and Langmuir Type-1, respectively. Cerium is desorbed from loaded adsorbents using acidic solutions.

The behaviour of oxidized and non-oxidized multiwalled carbon nanotubes in the adsorption of lanthanum(III) from aqueous solutions is described. Metal uptake is studied as a function of several variables such as the stirring speed of the system, pH of the aqueous solution and metal and nanomaterial concentrations. The experimental results are fitted to various kinetics and isotherm models, being the rate law fitted to the film diffusion and particle diffusion models, when the non-oxidized and the oxidized nanomaterials are used to remove lanthanum from the solution, respectively. Sulphuric acid solutions seem to be appropriate to recover the metal from La-loaded nanomaterials.

This paper describes the physico-chemical study of the adsorption of dysprosium (Dy³⁺) in aqueous solution onto two types of activated carbons synthesized from spent coffee ground. KOH activated carbon is a microporous material with a specific BET surface area of 2330 m²·g^-1 and pores with a diameter of 3.2 nm. Carbon activated with water vapor and N₂ is a solid mesoporous, with pores of 5.7 nm in diameter and a specific surface of 982 m²·g^-1. A significant dependence of the adsorption capacity on the solution pH was found, while it does not depend significantly neither on the dysprosium concentration nor on the temperature. A maximum adsorption capacity of 31.26 mg·g^-1 and 33.52 mg·g^-1 for the chemically and physically activated carbons, respectively, were found. In both cases, the results obtained from adsorption isotherms and kinetic study were better fit to a Langmuir model and a pseudo-second-order kinetics. In addition, thermodynamic results indicate that dysprosium adsorption onto both activated carbons is an exothermic, spontaneous and favorable process.

Preparation of a low-cost cellulose-based bioadsorbent from the cellulosic material extracted from the rose stems (CRS) was carried out; rose stems were considered agricultural wastes. After the required pretreatment of this waste, and its further treatment with an acidic mixture of acetic and nitric acids, the CRS product was yielded. The resulting bioadsorbent was characterized by several techniques, such as X-ray diffraction, which revealed diffraction maxima related to cellulose structure, whose calculated crystallinity index (CrI) was 75 %. In addition, Fourier Transform Infrared spectroscopy (FTIR), 13C Nuclear Magnetic Resonance (NMR), and X-ray Photoelectron Spectroscopy (XPS) showed signs of acetylation of the sample, also, the thermal properties of the solid was evaluated through Thermogravimetric Analysis (TGA). Scanning Electron Microscopy (SEM) showed cellulose fibers before and after the adsorption process, some particles with not regular shapes were also observed. The CRS bioadsorbent was used in the effective adsorption of valuable Tb(III) from aqueous solution. The adsorption data resulted in a better fit to the Freundlich isotherm, and pseudo-second-order kinetic models; however, chemisorption had not been ruled out. Finally, desorption experiments revealed a recovery of terbium ions with an efficiency of 97 % from terbium-loaded bioadsorbent.