Recent advances in the intercalation of metal complex cations in smectite clay minerals are leading to the development of new classes of selective heterogeneous catalysts. The selectivity of both metal-catalyzed and proton-catalyzed chemical conversions in clay intercalates can often be regulated by controlling surface chemical equilibria, interlamellar swelling, or reactant pair proximity in the interlayer regions. Also, the intercalation of polynuclear hydroxy metal cations and metal cluster cations in smectites affords new pillared clay catalysts with pore sizes that can be made larger than those of conventional zeolite catalysts.

https://science.sciencemag.org/content/sci/220/4595/365.full.pdf

Intercalated Clay Catalysts

Coagulation by hydrolysing metal salts

Preparation and catalytic properties of cationic and anionic clays

Many algae have immense capability to sorb metals, and there is considerable potential for using them to treat wastewaters. Metal sorption involves binding on the cell surface and to intracellular ligands. The adsorbed metal is several times greater than intracellular metal. Carboxyl group is most important for metal binding. Concentration of metal and biomass in solution, pH, temperature, cations, anions and metabolic stage of the organism affect metal sorption. Algae can effectively remove metals from multi-metal solutions. Dead cells sorb more metal than live cells. Various pretreatments enhance metal sorption capacity of algae. CaCl2 pretreatment is the most suitable and economic method for activation of algal biomass. Algal periphyton has great potential for removing metals from wastewaters. An immobilized or granulated biomass-filled column can be used for several sorption/desorption cycles with unaltered or slightly decreased metal removal. Langmuir and Freundlich models, commonly used for fitting sorption data, cannot precisely describe metal sorption since they ignore the effect of pH, biomass concentration, etc. For commercial application of algal technology for metal removal from wastewaters, emphasis should be given to: (i) selection of strains with high metal sorption capacity, (ii) adequate understanding of sorption mechanisms, (iii) development of low-cost methods for cell immobilization, (iv) development of better models for predicting metal sorption, (v) genetic manipulation of algae for increased number of surface groups or over expression of metal binding proteins, and (vi) economic feasibility.

Use of Algae for Removing Heavy Metal Ions From Wastewater: Progress and Prospects

Crystallisation is at the heart of various scientific disciplines, but still the understanding of the molecular mechanisms underlying phase separation and the formation of the first solid particles in aqueous solution is rather limited. In this review, classical nucleation theory, as well as established concepts of spinodal decomposition and liquid–liquid demixing, is introduced together with a description of the recently proposed pre-nucleation cluster pathway. The features of pre-nucleation clusters are presented and discussed in relation to recent modifications of the classical and established models for phase separation, together with a review of experimental work and computer simulations on the characteristics of pre-nucleation clusters of calcium phosphate, calcium carbonate, iron(oxy)(hydr)oxide, silica, and also amino acids as an example of small organic molecules. The role of pre-nucleation clusters as solute precursors in the emergence of a new phase is summarized, and the link between the chemical speciation of homogeneous solutions and the process of phase separation via pre-nucleation clusters is highlighted.

/pdf/pre-nucleation-clusters-as-solute-precursors-in-2bz3nzlo56.pdf

Pre-nucleation clusters as solute precursors in crystallisation

Studies of hydrolyzed aluminum chloride solutions. 1. Nature of aluminum species and composition of aqueous solutions

The mechanism of formation of layered aluminum hydroxides from aluminum chloride solution progressively neutralized by caustic soda has been studied by infrared spectroscopy, small-angle X-ray scattering, and 27Al high-resolution solid-state nuclear magnetic resonance. In the starting solution most of the cationic species belong to the so-called Al13 polymer (Keggin structure) made from 12 octahedra surrounding an aluminum tetrahedron. This polymer is stable in solution for hydrolysis ratio R = (OH)(Alt) 2.8, the hydrolysis mechanism is driven faster, leading to the formation of highly polymerized octahedral layers and to the disappearance of tetrahedral aluminum. For R = 3, the short-range order characteristic of bayerite is obtained very rapidly (⋍24 h). Thus crystalline Al trihydroxides are not formed by progressive condensation of flat hexamers made from Al octahedra but by solid-state structural rearrangement, without redissolution steps.

Mechanism of formation of aluminum trihydroxide from keggin Al13 polymers

Investigation of the hydrolysis of aqueous solutions of aluminum chloride. 2. Nature and structure by small-angle x-ray scattering

Adsorption of nonionic polyacrylamide on sodium montmorillonite: Relation between adsorption, ξ potential, turbidity, enthalpy of adsorption data and 13C-NMR in aqueous solution

L'agregation de particules colloidales de silice par des polycations d'hydroxyde d'aluminium est etudiee. Les variables physicochimiques comme le potentiel electrocinetique sont determinees en fonction de la nature chimique de la concentration et de la taille du floculant, et en fonction du PH de la suspension

F. Fiessinger

Papers

Studies of hydrolyzed aluminum chloride solutions. 1. Nature of aluminum species and composition of aqueous solutions

Mechanism of formation of aluminum trihydroxide from keggin Al13 polymers

Investigation of the hydrolysis of aqueous solutions of aluminum chloride. 2. Nature and structure by small-angle x-ray scattering

Adsorption of nonionic polyacrylamide on sodium montmorillonite: Relation between adsorption, ξ potential, turbidity, enthalpy of adsorption data and 13C-NMR in aqueous solution

Flocculation of silica colloids with hydroxy aluminum polycations. Relation between floc structure and aggregation mechanisms