Acetic acid leaching

Kumbasar RA and Tutkun O. Separation and concentration of galbum from acetic acid leach solutions containing various metal ions by emulsion t)fpe of bquid membranes using TOPO as mobile carrier. Hydrometallurgy 2004 75 111-121. 

Fig. 11.3 Vertical profiles of (a) dissolved iron (nmol kg" ) and (b) particulate iron (nmol kg" ) at the VERTEX-IV site (after Bruland et al. 1994). Eor particulate iron, filled circles represent the acetic acid leach-able fraction and open triangles represent refractory iron.

Many other difficulties arise in specific cases of solid-phase peptide synthesis, e.g., destruction of the tryptophan residue during acidolytic cleavage of resin-peptide bond, pyroglutamyl derivative formation, chain termination by acetylation with acetic acid leaching from teflon components, and formation of y-glutamyl peptides. Solutions to these problems provide the basis for much of the continuing work in the field. 

Another level of regulatory significance is the toxic characteristic leach procedure (TCLP) limit of a characteristic waste. A material which is a waste because of the TCLP is ha2ardous if a Hquor resulting from an 18-h leach in an acetic acid buffer exceeds 5 ppm (mg/L) lead in the leach Hquor. 

Pentaerythritol tetraacetate [597-71-7] M 304.3, m 78-79 . Crystd from hot water, then leached with cold water until the odour of acetic acid was no longer detectable. 

Waters Seawater (National Research Council Canada 1992) was collected in the North Atlantic Ocean at a depth of 10 m, 35 km southeast of Hahfax, Nova Scotia, Canada. The water was peristaltically pumped through cleaned polyethylene-hned ethyl vinyl acetate tubing and 0.45-pm acrylic copolymer filters. It was acidified to pH 1.6 with ultrapure nitric acid during its immediate transfer to 50-L acid-leached polypropylene carboys, previously conditioned with ultrapure water acidified to pH 1.6. The seawater was later homogenized in two linked 800-L polyethylene tanks in a clean room and immediately bottled in cleaned 2-L polyethylene bottles. Randomly selected bottles were used for analytical measurements. 

Regolith samples were collected from 68 sites along a transect extending from the CTSS in the SW of the island (near napa tou Pcjpiou), across Troodos and into the CTSS and fanglomates on the NE side of Troodos (near AsuKioaia). ICP-MS trace elements concentrations were determined following two conventional (sequential) leaches on the <2mm fraction of the upper (0-25 cm) and lower (50-75 cm) parts of the profile 1M ammonium acetate in pH 5 acetic acid and 1M hydroxylamine.HCI in pH 1 HCI. 

Nylon 6 can be prepared both by batch as also by continuous process. In batch process caprolactam, water (5-10%) and acetic acid (0.1%) are fed to a reactor under nitrogen and heated to 250°C at 15 atm for 12 hours. Steam formed is vented. The product contains about 10 per cent low Molecular weight products which are removed either by leaching with water at 85°C or by heating at 180°C at 0.005 atm pressure. 

The toxicity characteristic leaching procedure may be subject to misinterpretation if the compounds under investigation are not included in the methods development or the list of contaminants leading to the potential for technically invalid results. However, an alternative procedure, the synthetic precipitation leaching procedure (SPLP, EPA SW-846 Method 1312) may be appropriate. This procedure is applicable for materials where the leaching potential due to normal rainfall is to be determined. Instead of the leachate simulating acetic acid mixture, nitric and sulfuric acids are utilized in an effort to simulate the acid rains resulting from airborne nitric and sulfuric oxides. 

Another challenging and industrially important separation that utihzes pervapo-ration through zeolite membranes is acid removal from H2O. In this case, the zeolite must have a high Si/Al ratio due to leaching of A1 by the acid. Both Ge-ZSM5 and silicalite have demonstrated significant stability and separation capability for the removal of acetic acid from H2O [35]. 

Calcium serves as a reductant for such reactive metals as zirconium, thorium, vanadium, and uranium. In zirconium reduction, zirconium fluoride is reacted with culcium metal. The high heat of the reaction melts the zirconium. The zirconium ingot resulting is remelted undet vacuum for purilicatinn. Thorium and uranium oxides are reduced with an excess of calcium in reactors or trays under an atmosphere of argon. The resulting tnetals are leached with acetic acid tu remove the lime. 

A simple but effective means of preparing supported metal ion catalysts is to employ ion exchange resins. For example, a cobalt-exchanged H-type resin (Dowex 50) was shown43 to be an effective solid catalyst for the autoxidation of acetaldehyde to acetic acid at 20°C. No leaching of cobalt ions from the resin was observed and the catalyst was used repeatedly (5x) without any significant loss of activity. More recently the use of weak acid resins exchanged with cobalt ions as catalysts for the autoxidation of cyclohexane... 

Figure 7.2 Solid-state speciation in a crustal aerosol collected close to the Saharan Desert and an urban aerosol collected in the UK (Spokes et al., 1994). Results are expressed as a percentage of the total elemental concentration and obtained using a three stage sequential leach using the method of Chester et al. (1989). Stage one uses 1.0 M ammonium acetate to release loosely bound metals. Stage two involves addition of 1.0M hydroxylamine hydrochloride in 25% acetic acid to the residue to release metals held within the oxide and carbonate phases. Stage three uses nitric acid and hydrofluoric acid to break down the aluminosilicate lattice and release metals associated with the crustal fraction of the aerosol.

However, there was clear evidence for elution of Co from the resin during reaction. Since leaching of Co was promoted by the water formed in the autoxidation, some acetic anhydride was added to trap the water. Even then, leaching remained substantial, and the anhydride caused some polymerization. Clearly, since acetic acid is a corrosive medium and dissolves Co compounds well, it is probably impossible to find a supported equivalent of Co catalysis in acetic acid. Similar problems of leaching by acid might arise in the autoxidation of propionaldehyde to give perpropionic acid with Co- or Mn-exchanged resins as catalysts (169). 

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