Dilute Mineral Acid Research Articles

The physical chemistry of the precipitation stripping process for removing iron (III) from carboxylate solutions with dilute Sulphuric Acid

Precipitation stripping is a single-stage process for stripping a metal from a loaded liquid cation exchanger with dilute mineral acid while simultaneously precipitating a hydrolyzed phase. The process has potential applications for removing iron from hydrometallurgical process streams; iron (III) can be stripped from carboxylate solutions with dilute H 2SO 4 (10–40 g/l), at 100°C under atmospheric pressure, to give goethite or basic sulphates. Experimental results for precipitation stripping are summarized. The thermodynamics of the process are examined and equilibrium constants for the precipitation stripping process are estimated at 25°C and 100°C. For the formation of goethite and hematite, these constants are very high at both temperatures. This indicates that iron (III) can only be extracted in reasonable concentrations by carboxylic acids before precipitates have nucleated, or when the metastable phase Fe (OH) 3 is present. The sluggish kinetics of Fe(III) hydrolysis and precipitation favour extraction at 25°C. At 100°C, however, goethite and hematite precipitate more rapidly, which drives the precipitation stripping process to near completion. The structure of the iron carboxylate complexes within the organic phase is discussed, along with the influence of these structures on the kinetics of stripping and the nature of the hydrolysis products.

Aluminium contamination from fluoride assisted dissolution of metallic aluminium

Trace amounts (μg g −1 quantities) of fluoride ion are found to catalyse the dissolution of metallic aluminium in very slightly acidic or alkaline aqueous media. Possibly hazardous levels of aluminium could get leached from cooking utensils if fluoridated water or fluoride rich foodstuffs are used. The fluoride assisted corrosion of aluminium is most dramatic in oxalic, tartaric acids or sodium bicarbonate. Carbon dioxide also corrodes aluminium in the presence of the fluoride ion, generating colloidal hydrated aluminium oxide which is readily soluble in dilute organic and mineral acids.

Trace metal fouling and cleaning of seawater R.O. membranes

The low concentrations of heavy metals in seawater are very often ignored as potential foulants for RO membranes in seawater desalination. Cumulative deposition of such metals may result, which is difficult to remove by conventional cleaning techniques. Destructive tests on hollow fibre membranes, followed by a mass balance exercise during routine operation of the Ghar Lapsi seawater RO plant in Malta, revealed the existence of trace metal depositions. The metals iron, copper, zinc, chromium, lead and vanadium were detected on these membranes. Dilute mineral acids were found to be the only effective cleaning agents in ‘in vitro’ experiments. A more efficient pre-treatment and cleaning technique must therefore be investigated to control these deposits.

Studies of selective adsorption resin. XXIV. Preparation and properties of macroreticular chelating resins containing both polyethylenepolyamine side chains and mercapto groups

The macroreticular chelating resins containing both polyethylenepolyamine side chains and mercapto groups were prepared by the reaction of 2,3-epithiopropyl methacrylate-divinylbenzene macroreticular copolymer beads with polyethylene-polyamine. The adsorption behavior of metal ions on the obtained resins was then investigated. The amination of the macroreticular copolymer beads could effectively be carried out by treatment of the polymer beads with polyethylenepolyamine in organic solvent (benzene, terahydrofuran) or in the absence of organic solvent at 80°C or 100°C for 60 min. It was found that the adsorption capacity of the resins for metal ions is not only affected by the ion exchange capacity of the resins but also by the porosity of the resins. Hg2+, Ag+, and Cu2+ were effectively adsorbed on the resins even at a pH below 3, whereas Co2+, Ni2+, and Cd2+ were adsorbed at a pH above 3, Mn2+ at a pH above 7, and Ca2+ at a pH above 8. These metal ions adsorbed on the resins could easily be eluted with dilute mineral acid solution or dilute mineral acid solution containing thiourea.

Role of polyacrylate starch copolymer in water sorption

AbstractWater sorbence by saponified polyacrylonitrile‐grafted polysaccharides was studied in relation to practical end uses. Graft copolymers prepared from wheat flour, corn flour, cotton wool, and rayon fibers swelled to a gel, exhibiting a 10‐ to 20‐fold increase in sorbency over the starting materials. A further enhanced water capacity was obtained when homopolymer was not removed. Soaking the wheat flour copolymer in salts or dilute mineral acid nullified the enhanced water sorbence, which could be reversible restored by neutralization of acrylic acid functions with alkali. Swelling the copolymer in aqueous D‐glucose did not impair its water capacity. The mechanism of swelling to a gel appears to involve electrolyte osmotic pressure generated by a Donnan equilibrium. Grafting starch elevated its heat of water vaporization above that of pure water, and increased its capacity to absorb water from ethanol‐water vapor at 40° above that of native starch. At higher temperatures, however, the dehydrating capacity decreased to that of native flour.

Studies of selective adsorption resin. XXIV. Preparation and properties of macroreticular chelating resins containing both polyethylenepolyamine side chains and mercapto groups

AbstractThe macroreticular chelating resins containing both polyethylenepolyamine side chains and mercapto groups were prepared by the reaction of 2,3‐epithiopropyl methacrylate‐divinylbenzene macroreticular copolymer beads with polyethylene‐polyamine. The adsorption behavior of metal ions on the obtained resins was then investigated. The amination of the macroreticular copolymer beads could effectively be carried out by treatment of the polymer beads with polyethylenepolyamine in organic solvent (benzene, terahydrofuran) or in the absence of organic solvent at 80°C or 100°C for 60 min. It was found that the adsorption capacity of the resins for metal ions is not only affected by the ion exchange capacity of the resins but also by the porosity of the resins. Hg2+, Ag+, and Cu2+ were effectively adsorbed on the resins even at a pH below 3, whereas Co2+, Ni2+, and Cd2+ were adsorbed at a pH above 3, Mn2+ at a pH above 7, and Ca2+ at a pH above 8. These metal ions adsorbed on the resins could easily be eluted with dilute mineral acid solution or dilute mineral acid solution containing thiourea.

‘Gel collapse’ in the saponified starch-g-polyacrylonitrile/water-alcohol system

A sample of starch-g-polvacrylonitrile (grafting ratio 82%) has been prepared at 303 K using the Mn 3+ complex ion as initiator in aqueous acid solution with gelatinized starch as substrate. Subsequent alkaline hydrolysis converts the nitrile groups to carboxamide (∼30%) and sodium carboxylate (∼70%) groups. The swelling of the copolymer formed which retains about 700 g water per g of dry copolymer, has been studied in alcohol/water mixtures of increasing alcohol content at 294, 304 and 314 K. The liquid retention vs. alcohol concentration indicates one minor transition for ethanol/water mixtures and possibly two small transitions for methanol/water mixtures. The main transition for both alcohol/water mixtures is a collapse of the gel at 50–60 volume% ethanol and 60–70 volume% methanol, respectively. Increasing the temperature from 294 to 314 K increases the liquid retention and moves the transitions to higher alcohol concentrations by 5–10 volume%. When the starch copolymer is hydrolysed in dilute mineral acid to remove the starch moiety, the retention values increase by a factor of approximately 3 for both pure water and alcohol/water mixtures. The retention vs. methanol concentration curves show three transitions which are similar to those of the starch copolymer before acid hydrolysis. A tentative interpretation of the transitions is proposed and discussed.

Synthesis, structural characterization, and reactions of closo-rhodacarborane anions containing a formal d8 metal vertex

Abstract : Deprotonation of three neutral closo- hydrido complexes (L)2-H-RhC2B9H11) under carefully controlled reaction conditions yields the corresponding isomeric (closo-L2RhC2B9H11)- species. Two of these have been structurally characterized: K(18-crown-6) (closo-3,3-(PPh3)2-3,1,2-RhC2B9H11).C4H8O.H20, 2a, (Me4N) (closo-2,2-(PPh3)2-2,1,7-RhC2B9H11), 2b. Salts of 2a, 2b, and (closo-2,2-(PPh3)2-2,1,12-RhC2B9H11)-, 2c were treated with dilute mineral acids in ethanol to produce the neutral hydrido-closo complexes and with pi-acceptor ligands L = CO or C2H4 to produce the corresponding (closo-(PPh3)(L)-RhC2B9H11) salts. (Author)

Hydrolysis of F-octanesulfinic acid

F-alkanoic acids are useful functional fluorochemicals that can be produced in modest yields by electrochemical fluorination (ECF). In contrast, F-alkanesulfonyl fluorides, R fCF 2SO 2F, are readily available in good yields by the ECF method. The conversion of R fCF 2SO 2F to R fCO 2H is desirable under mild conditions. We have found that acid hydrolysis of F-octanesul finic acid, C 8F 17SO 2H, obtained by the reduction of the sulfonyl fluoride, C 8F 17SO 2F, with diluted mineral acids including 10% H 2SO 4, yielded primarily F-octanoic acid. Varying amounts of F-octanesul fonic acid, C 8F 17SO 3H, are also formed. The hydrolysis conditions are far milder than those used by Ma et al. (CA 96:6660u). Studies by Huang et al. (J. Fluor. Chem. (1983) 23, 229) have attributed desulfoxylation of the sul finic acid to a redox reaction. Our studies suggested that a hydrolysis rather than a redox reaction is taking place.

Kinetics of Hydrolyses of Sorghum Molasses with Dilute Mineral Acids and Oxalic Acid and Melibiose with Oxalic Acid

ABSTRACTInvestigations were carried out on the kinetics of hydrolyses of sorghum molasses with dilute mineral acids and oxalic acid and melibiose with oxalic acid at relatively high temperatures. Kinetic equations for hydrolysis of sorghum molasses and melibiose have been derived from the experimentally determined hydrolysis rate constants as functions of the acid concentration and temperature. It has been shown that the hydrolysis activity of oxalic acid is weaker than those of hydrochloric and sulfuric acid, and that the second hydrogen atom in oxalic acid does not significantly participate in hydrolysis.

Selective absorption of copper, nickel, cobalt and other transition metal ions from sulfuric acid solutions with the chelating ion exchange resin XFS 4195

Data for the distribution of a number of common metal cations between sulfate solutions and the chelating ion exchange resin XFS 4195 are presented. The effects of pH and metal ion concentration are shown, and some data are presented on the effects of sulfates on absorption and on the selectivities for various pairs of ions. The general order of affinity of the resin for ions is Cu(II) ⪢ UO 2(VI) > Ni(II) > Fe(III) > Zn(II) > Co(II) > Cd(II) > Fe(II). Except for copper, which is strongly absorbed even in 3 N sulfuric acid, absorption of all metal ions is relatively low in acid solutions below pH 1, but rises to a maximum at about pH 3. Elution of most metal ions is therefore readily accomplished with dilute mineral acid; elution of copper requires ammonium hydroxide.

Ultrastructural differences between wall apices of growing and non-growing hyphae ofSchizophyllum commune

Newly synthesized chitin at the hyphal apex ofSchizophyllum commune was shown to be highly susceptible to chitinase degradation and solubilization by dilute mineral acid. With time this chitin became gradually more resistant to these treatments. With a combination of the shadow-cast technique and electron microscopic autoradiography it could be shown that this process occurred as the newly synthesized chitin moved into subapical parts of growing hyphae but also in non-growing apices which had ceased growth after incorporation of theN-acetyl[6-3H]glucosamine. These results are in agreement with a model which explains apical morphogenesis by assuming that the newly synthesized wall material at the apex is plastic due to the presence of individual polymer chains but becomes rigidified because of subsequent physical and chemical changes involving these polymers.

Generation of surface active acids in crude oil for caustic flooding enhanced oil recovery

The process of recovering residual oil from an oil reservoir, by alkaline flooding relies on soap formation by the reaction of the alkali and free long-chain organic acids in the crude oil. In this study, dilute mineral acids were used to liberate additional new organic acids from their nonreactive compounds such as esters, amides, and acid-base complexes present in the crude oil. This was accompanied by an observed enhanced or regenerated interfacial activity of the oil. This acid pretreatment method may be applied to oil reservoirs which have been exhausted by previous alkaline floodings to regenerate activity in the residual oil or to reservoirs never exposed to any alkali contact to give the subsequent alkaline flooding a better first-round recovery. The major technical problem anticipated in applying this process to actual reservoirs is the consumption of acid by th reservoir rock. An analysis was done that showed that sandstone reservoirs with low clay and carbonate content are amenable economically to such an acid treatment. Slug sizes for the acid and water buffer slugs have been estimated using a simple diffusion, convective dispersion model to ensure that the acid and alkaline slugs do not mix.

Sorption of some metal cations by a modified biopolymer based on the mycelium of Penicillium chrysogenum

Three types of a modified biopolymer based on the mycelium of Penicillium chrysogenum were evaluated as to their sorption characteristics for Hg2+, Pb2+, Cu2+ and Cd2+. Their useful and total sorption capacities were calculated from their respective breakthrough curves. The highest sorption capacity was recorded for Hg2+. Evidence is presented that the retained metals can be easily eluted with diluted mineral acids.

The preparation and properties of chelates of transition metal ions with the homopolymer and copolymers of p‐vinylbenzoylacetone

Abstractp‐Vinylbenzoylacetone (VBA) was prepared by the condensation of p‐vinylacetophenone and ethyl acetate. This monomer was homopolymerized and copolymerized with acrylamide or maleic anhydride to produce polymers which would chelate substantial amounts of transition metal ions such as Cu2+, Ni2+, Co2+, Eu3+, and VO2+. In the case of the Cu2+ and Ni2+ chelates, about 80–90% of the metal ion could be eluted by dilute mineral acids. The resulting eluted products apparently have a somewhat porous structure because they are capable of rechelating these ions from water solution, even though the solid homopolymer which had not been chelated and eluted is too hydrophobic to chelate very much metal ion from water solution. The eluted Cu2+ chelate readily reaccepted Cu2+ ions from water solution and discriminated against Ni2+ almost completely. However, the eluted Ni2+ chelate would reaccept both Cu2+ and Ni2+ ions, but exhibited a strong preference for Cu2+ ions in competitive batch experiments. The VO2+ chelate was an effective heterogeneous phase catalyst for the epoxidation of allyl alcohols such as geraniol with tert‐butylhyroperoxide. The chelate was stable under these oxidative conditions and could be recovered unchanged and reused.

Changes in Extractable Metal Concentrations During Storage of Surface Water Samples Containing Sediments1

ABSTRACT: Changes in metal concentrations during storage of acidified water samples were studied. Water samples with high concentrations of suspended sediment were collected from the Fraser River, British Columbia. These samples were analyzed for “extractable” metals, which are defined to be the dissolved metals plus those metals extracted from suspended sediment by dilute mineral acid. Concentrations of extractable Cu, Fe, Pb, Zn, Ni, Co, Mn, and Cd were determined over time. Metal concentrations in these water samples were not stable and showed significant increases throughout the storage period. These results suggest that the extractable metal technique is inappropriate for the analysis of water samples containing suspended sediment.

Vinyl ether hydrolysis. XV. Methyl β,β-di-tert-butylvinyl ether: buttressing steric effects

The highly congested molecule, methyl β,β-di-tert-butyl vinyl ether, undergoes reaction in dilute aqueous mineral acid solutions by a normal vinyl ether hydrolysis mechanism and gives an unrearranged aldehyde product. The tert-butyl groups retard the rate of hydrolysis, but the effect of cis and trans substituents is not cumulative; this is attributed to a repulsive nonbonded interaction, relieved in the course of reaction, between the ether oxygen atom and the cis-tert-butyl group buttressed by the trans-tert-butyl group.

Detection of primary and secondary amines in energy-related materials using an element-selective glow-discharge detector

Mutagenic primary polycyclic aromatic amines present in shale oil and synthetic crudes may be readily detected by a simple derivatization and Chromatographic procedure. Nitrogenous bases and amines are extracted from the sample with dilute mineral acid and derivatized with trifluoroacetic anhydride. The derivatized amines are separated by gas chromatography and specifically detected using a glow-discharge detector tuned to an emission wavelength of fluorine. Under these conditions, the aromatic nitrogenous bases, such as acridine, are not detected even though they are present in the sample. As little as 14 ng of fluorine, arising from the derivative of 33 ng of 2,4,6-trimethylaniline, can be detected. The selectivity of the glow-discharge detector for derivatized amines vs. nonderivatized aromatic nitrogenous bases was estimated to be a minimum of 200:1.

Fractionation of gamma-emitting fission products absorbed by red kidney beans ( Phaseolus vulgaris L.)

The gamma-emitting fission product nuclides 106Ru, 125Sb, 137Cs and 144Ce that accumulated in the edible pods of bean ( Phaseolus vulgaris L.) plants grown in nutrient culture were subjected to chemical fractionation. The results indicated that the largest fraction of 106Ru, 125Sb and 144Ce was associated with ionic forms including salts of organic acids, phosphates, carbonates and some protein-bound forms extracted with dilute mineral acids (acid fraction). The association of these radionuclides with lipids including lipophyllic pigments, free amino acids and amino sugars (ethanol fraction) was next in significance. The association of 137Cs was, however, greater with the ethanol fraction than with the acid fraction. Considerably reduced amounts of the fission products were present in the pectates, proteins, polysaccharides and nucleic acids.

Europium(II) Heptaphosphide EuP7 [1] Europium(II)heptaphosphid EuP7 [1

The novel polyphosphide EuP7 was prepared under controlled conditions by the reaction of the elements in salt melts at 750-800 K. EuP7 forms black prismatic crystals not attacked by diluted mineral acids and bases. The thermal decomposition yields EuP3 at 700 K and in further steps EuP2, Eu3P4 and EuP, respectively. According to the crystal structure as well as the electrical, optical and magnetic properties EuP7 is a semiconductor (EG = 0.9 eV; EG (vert) = 1.1 eV) with divalent europium (μ = 7.55 B.M.). The compound crystallizes in the monoclinic space group P21/n with a = 1148.8(7) pm, b = 570.0(3) pm, c = 1061.0(6) pm, and β= 106.08°(5); (X-ray diffraction data; 1479 hkl, R = 0.031). The P-atoms are connected (P-P) = 218.0-223.5 pm) to a 2-dimensional infinite polyanionic structure with homonuclear 3-bonded and 2-bonded P-atoms in the ratio 5:2. The polyanionic network contains P6-rings (chair conformation) as well as P8-rings and P10-rings. The Eu-atoms are bonded to 9 P-atoms (1,4,4-polyhedra) with bond distances ranging from 306.6 to 326.6 pm. The Eu-atoms complete the tetrahedral environment of the P-atoms