Adsorption of fatty acids on fine mineral particles as a purification method of industrial wastewaters

The problem of fines disposal and utilization that has to be faced from most of the mineral processing plants, in relation with the removal of fatty acids (reagents that constitute usual anionic collectors and could be possibly found in flotation plant waters) led to the study of the adsorption of later on fine particles, being in this case magnesite and dolomite. Another main application of this work is in the separation of fines (at sub‐sieve size range) by flotation. Sodium oleate and a commercial tall oil fatty acid were selected in the present. Common parameters and their effect on adsorption were carefully looked at, including the pH of solution and concentration. The presence of modifying reagents (as sodium hexametaphosphate, pyrophosphate and carboxymethyl cellulose) was also examined.     

Application of flotation for the separation of metal-loaded zeolites

Several industrial wastewater streams may contain heavy metal ions, which must be effectively removed, before the discharge or reuse of treated waters could take place. Different bonding materials, presenting selectivity and fast reaction kinetics for the removal of metals, have been examined for this purpose. The objective of the present paper was to investigate the application of dispersed-air flotation for the separation of metal-loaded sorbents. Two similar zeolite samples were applied as effective bonding agents for the removal of zinc, a toxic metal commonly found in many industrial wastewaters. This combined process, termed sorptive flotation, involves the preliminary scavenging of metal ions, by using the appropriate sorbent particles (usually present as ultrafine particulates), followed by flotation for the effective separation of them. The obtained results were very promising, as both metal and sorbent were effectively removed/separated from the dispersion.     

Removal of chromium (VI) from water streams: a thermodynamic study

The chemical speciation of water solutions containing chromium oxyanions in various ratios is calculated (with the aid of available computer code Mineql Plus, Geochemist Workbench and Visual Minteq) and discussed. The effect of solution pH, total concentration of each species studied, and the presence of other species in solution are calculated and presented in the form of thermodynamic speciation diagrams. Electrochemical diagram (correlating pH to Eh) has been calculated as well. The conditions of Cr(VI) reduction to Cr(III) and the subsequent solid phase precipitation are given as a function of redox potential and pH. Surface reactions that might occur between the chromate ions in the solution and redox couples as Fe²⁺/Fe³⁺ on the surface of sorbents are also discussed. Moreover, experimental sorption data of hexavalent chromium onto synthetic magnetite are presented and discussed with the aid of the calculated diagrams. A mechanism is elucidated for the efficient removal of Cr(VI) from water streams at low pH values, and zeta potential data of synthetic magnetite with and without Cr(VI) are presented, which agree well with the mechanism proposed.     

Sonochemical decomposition of natural polyphenolic compound (condensed tannin)

Sonochemical treatment of grape condensed tannin was studied with the aim to destroy phenolic constituents, using ultrasonic frequency of 20 kHz in the presence and in the absence of hydrogen peroxide (H2O2), as an oxidative agent. Various pH, H2O2 concentration and temperature combinations were used in order to investigate the role of these parameters in the studied process. In order to estimate the effect of ultrasound, similar experiments were conducted in terms of pH, H2O2 concentration and temperature conditions, but without sonication. In all cases the presence of H2O2 was resulted in considerably higher removal of total phenolics (TP). It was observed that pH and temperature present also a significant effect on TP removal in the presence of H2O2, both with and without sonication. Under similar experimental conditions higher reaction rates, concerning TP removal, were obtained in the presence of ultrasonic irradiation, than in its absence.