Liquid phase hydrogenation of crotonaldehyde over Pt/SiO2 catalysts

The dependence of the catalytic properties of Pt/SiO2 catalysts for the hydrogenation of crotonaldehyde on the hydrogen pressure, the reaction temperature, the nature of the solvent and the presence of several additives were investigated. Strong deactivation of the catalysts mainly caused by decarbonylation of crotonaldehyde and irreversible adsorption of CO was observed. The initial activity of the deactivated catalysts is regained by oxidation of the adsorbed CO to CO2 by purging with air. The selectivity to crotylalcohol increased with increasing number of turnovers per metal site. This is explained with preferential blocking of the nonselective sites on the metal crystallites by CO and by a slow surface modification of the aging catalyst with organic deposits. The overall rate and the selectivity to the saturated aldehyde are markedly enhanced by an increase in hydrogen pressure and by a decrease in reaction temperature. The addition of modifiers such as potassium acetate, triphenylphosphine and thiophene had only little influence on the activity and the selectivity of the catalysts

Role of Mixed Collector Systems in Selective Separation of Albite from Greek Stefania Feldspar Ore

The adsorption behaviour of mixed cationic alkyl diamine and anionic sulfonate/oleate collectors and a combined cationic-anionic collector, N-tallow 1, 3-propane diamine dioleate (Duomeen TDO) at acidic pH values on albite and quartz minerals was investigated through Hallimond flotation, electrokinetic and diffuse reflectance FTIR studies. The reagent schemes are tested in bench scale flotation for the separation of albite from Greek Stefania feldspar ore. The single mineral flotation tests showed the feasibility of selective albite flotation from quartz at pH 2 where the doubly positively charged collector species adsorb on albite but not on quartz. However, the adsorption behaviour of mixed collectors on albite and quartz at the same pH value, as evidenced from zeta-potential and FTIR studies, is almost similar. The IR spectra show the co-existence of neutral oleic acid together with charged amine species at low pH values. The bench scale flotation results indeed showed that selective albite flotation takes place only after desliming the feed material. An albite concentrate exceeding 10 Wt% Na2O content is produced from a material containing about 6.5 wt% Na2O, where an albite product more than 9 wt% Na2O is considered to be valuable

Froth Flotation and its Application to Concentration of Low Grade Iron Ores

Froth flotation is a process used to separate minerals, suspended in liquids, by attaching them to gas bubbles to provide selective levitation of the solid particles. It is most extensively used process for the separation of chemi-cally similar minerals, and to concentrate ores for econo-mical smelting. Flotation is a selective process and can be used to achieve separation from complex ores such as lead-zinc, copper- zinc etc.Initially developed to treat the sulphides of copper, lead, and zinc, the field of flotation has now expanded to include oxides, such as hematite and cassiterite, oxidised minerals, such as mala-chite and cerussite, and non-metallic ores, such as fluo-rite, phosphates, and fine coal

Adsorption Mechanism of Longchain Alkylamines on Quartz and Albite

The mechanism of adsorption of long-chain alkylamines at pH 6-7 onto quartz and albite using the direct methods of FTIR and XPS spectroscopy. The spectroscopic data were correlated with the data of indirect methods of zeta-potential measurements and Hallimond flotation results. It was shown from infrared spectra that the amine cation forms strong hydrogen bonds with surface silanol groups. The XPS spectra revealed the presence of molecular amine together with the protonated amine on silicate surface. Based on these observations, a model of successive two-dimensional and three-dimensional precipiation was suggested to explain amine adsorption on silicate surface

Recovery of clean coking coal from difficult-to-wash low volatile coking coal fines of Jharia coalfield by multi gravity separator

Multi gravity separator (MGS) is a centrifugal gravity separator deployed for beneficiation of fine particles with relatively low concentration. It is for the first time, that a statistical tool was engaged to evaluate effects of the most influencing process variables and their actual impact upon the performance of MGS with respect to its potential to clean the difficult-to-wash low volatile coking (LVC) coal fines. Characteristics of LVC coal sample was analysed and discussed in terms of physical properties, petrographic composition, washability, XRD and SEM analysis. Three different feed sizes such as –500 μm, –250 μm and –150 μm were used for assessing the separation mechanism and efficacy of MGS along with three different process variables such as drum speed, shaking amplitude and wash water rate to study and ascertain the most efficient experimental design for obtaining optimal result. Results revealed that drum speed and feed size turned out to be most significant parameters for reduction of ash concentration. In design of experiments, clean coal ash, combustible recovery and separation efficiency were considered as response functions. Material balance for MGS unravelled that about 74% clean coal produced with 10% ash reduction from the feed ash of 32.8% could be achieved in single stage, in optimized process conditions

Flotation Of Quartz And Hematite: Adsorption Mechanism Of Mixed Cationic/Anionic Collector Systems

Using pure quartz and hematite minerals, the adsorption mechanism of mixed cationic/anionic reagent schemes was investigated through Hallimond flotation studies. The flotation response of quartz and hematite independently with cationic and anionic collectors as well as with mixed cationic/anionic collector systems is assessed. The flotation response as a function of pH and collector concentration was investigated. The single mineral flotation tests in the presence of anionic collectors, quartz does not respond to flotation but the C12 amine flotation of quartz was observed to be pH and concentration dependent. It was observed that hematite flotation recovery is maximum at acidic pH with sodium dodecyl sulphate (SDS), neutral pH with oleate, and at basic pH about 9.5 with C12 amine. Flotation results with both quartz and hematite indicate an increased adsorption of cationic collector in the presence of anionic collector apart from its own co-adsorption. The incorporation of oleate in between C12 amine molecules decreases the electrostatic head-head repulsion and thereby increasing the adsorption of C12 amine due to attractive tail-tail hydrophobic bonds, besides forming a closely packed adsorbed layer enhancing the hydrophobicity. The increase in oleate concentration beyond C12 amine concentration leads to the formation of soluble diamine-oleate complex / precipitate and the adsorption of these species decreased the flotation since the alkyl chains are in chaotical orientation with a conceivable number of head groups directing towards the solution phase

Role of Mixed Cationic/Anionic Collector Systems on Hematite Flotation

The adsorption mechanism of mixed cationic alkyl diamine and anionic sulphate/oleate collectors was investigated on hematite through Hallimond flotation studies. The flotation response of hematite independently with cationic and anionic collectors and with mixed cationic/anionic collector systems is assessed. The Hallimond flotation response of hematite as a function of pH and collector concentration was investigated. The study revealed that hematite flotation recovery is maximum at acidic pH with sulphate, neutral pH 6-7 with oleate, and at basic pH about 9.5 with diamine. It is the first time that the hematite flotation results show increased adsorption of cationic collector in the presence of anionic collector apart from its own co-adsorption. The presence of oleate increased the diamine adsorption due to a decrease in the electrostatic head-head repulsion between the adjacent surface ammonium ions and thereby increasing the lateral tail-tail hydrophobic bonds. The increase in oleate concentration beyond diamine concentration leads to the formation of soluble 1:2 diamine-oleate complex or precipitate and the adsorption of these species decreased the flotation since the alkyl groups of these adsorbed species are randomly oriented at the surface

Optimization of Process Parameters for Flowing Film Concentration of Ground Printed Circuit Boards

Printed circuit boards, incorporated in most electrical and electronic equipment, contain valuable metals such as Cu, Ni, Au, Ag, Pd, Fe, Sn and Pb, etc. The circuit boards are rich in metal content and the need for processing these wastes to extract the metals values and remove the non-metallic constituents has been felt all over the world. It was evident from size-wise chemical analysis of the ground PCBs that the particulate system is quite rich in metal value with about 23% of the total powder being metallic. It contained 12.8% Cu, 2.4% Pb, 1.2% Sn, 2.5% Al and 0.5% Ni. This paper summarizes the effect of operating variables of crushed PCB waste using Wilfley Table. Detailed experimentation has been performed with crushed printed circuit boards according to a Box-Behnken design of experiments to establish the influence operating variables on the separation performance. The optimized conditions for maximizing the yield of the metal values with respect to the specified grade of the concentrate were discussed in the light of the experimental results