Acid-producing potential

Estimation and prediction as to whether waste rock and tailings will produce acid mine drainage (AMD) are precursory to environmental certification, and therefore are a critical step in mine development. Kinetic tests are carried out using a cell or column that are operated over a period of typically 1 year, whereas static tests are a onetime measurement to determine the acid producing potential (AP) and... 

A direct determination of acid-producing potential is the rapid pyrite oxidation technique utilizing 30% H202, The actual acid produced during pyrite oxidation by H202 is termed potential acidity (Sobek et al., 1978). The technique determines the amount of acid produced during complete oxidation of Fe2+ and S2 of pyrite as follows ... 

Numerous types of static tests have been developed, and some of the laboratory procedures and the variety of tests or their individual developments have been described in various publications, such as those by MEND (1991), Lawrence and Wang (1997), Morin and Hutt (1997), White et al. (1999), and Jambor (2003). By far the most widely adopted static test, both for metalliferous and coal deposits, is the acid-base account (ABA) of Sobek et al. (1978). As is implied by its name, ABA involves a determination of the acid-producing potential (AP) of a sample, and a determination of the base that is potentially releasable the latter is generally referred to as the neutralization potential (NP). The two chemically determined values therefore provide a net accounting of the expected behavior during weathering. A common form of expressing the result is to obtain the net NP (NNP) by simple subtraction of the two chemically determined values ... 

Characterization of long-term reactivity and bioavailability of heavy metals in sediments can be performed by (i) acid-producing potential (APP Kersten and Fbrstner... 

These experimental test procedures, together with calculations of the acid-producing potential (APP) and acid-neutralizing capacity (ANC), are characteristic tools for the medium- and long-term prediction of metal release from all types of waste materials. Application of such prognostic tool will become even more important, when the rate of waste material utilization/ recycling is enhanced (in Germany up to 100% by the year 2020), and will intensify the contact of the secondary products with the soil environment. 

Transformation of reactive organic substances will result in variations of redox potential, pH-values, as well as concentrations of inorganic ions and dissolved organic carbon the latter two components may enhance complexation of metals. Regarding the subsequent consideration, acid-producing potentials derived from oxidation of sulphides and organic matter are of prime importance. 

THPC—Amide Process. The THPC—amide process is the first practical process based on THPC. It consists of a combination of THPC, TMM, and urea. In this process, there is the potential of polymer formation by THPC, melamine, and urea. There may also be some limited cross-linking between cellulose and the TMM system. The formulation also includes triethanolamine [102-71-6J, an acid scavenger, which slows polymerization at room temperature. Urea and triethanolamine react with the hydrochloric acid produced in the polymerization reaction, thus preventing acid damage to the fabric. This finish with suitable add-on passes the standard vertical flame test after repeated laundering (80). 

Virtually all metallurgies can be attacked by corrosive bacteria. Cases of titanium corrosion are, however, rare. Copper alloys are not immune to bacterial attack however, corrosion morphologies on copper alloys are not well defined. Tubercles on carbon steel and common cast irons sometimes contain sulfate-reducing and acid-producing bacteria. Potentially corrosive anaerobic bacteria are often present beneath... 

In general, however, for titanium immersed in acid solutions, potentials above zero on the saturated calomel scale are conducive to the formation of protective oxide, while at certain negative potentials hydride films, which also confer some protection, can be formed. Between the potential at which a continuous hydride film is formed and that at which protective oxide films appear, soluble titanium ions are produced and rapid corrosion ensues. 

An increase in conductivity usually increases T because it increases the proportion of polarisation in the total cell potential difference and lowers the ratio ( V A )/( V - AEj). Changing the conductivity of an acid copper bath with sulphuric acid produced the following result (291 A/m average c.d., P = 5) ... 

Organophosphate Ester Hydraulic Fluids. Organophosphate esters are made by condensing an alcohol (aryl or alkyl) with phosphorus oxychloride in the presence of a metal catalyst (Muir 1984) to produce trialkyl, tri(alkyl/aryl), or triaryl phosphates. For the aryl phosphates, phenol or mixtures of alkylated phenols (e.g., isobutylated phenol, a mixture of several /-butylphenols) are used as the starting alcohols to produce potentially very complex mixtures of organophosphate esters. Some phosphate esters (e.g., tricresyl and trixylyl phosphates) are made from phenolic mixtures such as cresylic acid, which is a complex mixture of many phenolic compounds. The composition of these phenols varies with the source of the cresylic acid, as does the resultant phosphate ester. The phosphate esters manufactured from alkylated phenylated phenols are expected to have less batch-to-batch variations than the cresylic acid derived phosphate esters. The differences in physical properties between different manufacturers of the same phosphate ester are expected to be larger than batch-to-batch variations within one manufacturer. 

These reactions, which are believed to occur predominantly inter-molecularly, are capable of producing intermediates which hold some potential as precursors for important chemical products. For example, metathesis of olive oil, which consists chiefly of triglycerides of oleic acid, produces the glyceride of 9-octadecene-l,l8-dioic acid from which can be obtained, after saponification, acidification, and low-temperature crystallization, the free acid, which can be transformed by intramolecular condensation to civetone. 

An ideal derivation would be via direct fluorination of Re and hydrolysis of ReF7 to perrhenic acid, especially since A/2f (Re207) has been determined by oxygen combustion of Re. However, ReF6 is the main fluorination product under normal conditions. It seems that further work on iodine fluorination to produce enhanced yields of the hepta-fluoride, and the hydrolysis of IF7 to periodic acid, is potentially the best route for improving the AHf(F( aq)) value. 

Two possible mechanisms are proposed. Primarily the enol radical cation is formed. It either undergoes deprotonation because of its intrinsic acidity, producing an a-carbonyl radical, which is oxidized in a further one-electron oxidation step to an a-carbonyl cation. Cyclization leads to an intermediate cyclo-hexadienyl cation. On the other hand, cyclization of the enol radical cation can be faster than deprotonation, producing a distonic radical cation, which, after proton loss and second one-electron oxidation, leads to the same cyclo-hexadienyl cation intermediate as in the first reaction pathway. After a 1,2-methyl shift and further deprotonation, the benzofuran is obtained. Since the oxidation potentials of the enols are about 0.3-0.5 V higher than those of the corresponding a-carbonyl radicals, the author prefers the first reaction pathway via a-carbonyl cations [112]. Under the same reaction conditions, the oxidation of 2-mesityl-2-phenylethenol 74 does not lead to benzofuran but to oxazole 75 in yields of up to 85 %. The oxazole 75 is generated by nucleophilic attack of acetonitrile on the a-carbonyl cation or the proceeding enol radical cation. 

Another method of preventing acid mine drainage is to construct barriers around the mine itself. The most important single source of AMD are abandoned coal mines. In some cases, the entrances to those mines can be sealed or barriers can be constructed to prevent the outflow of acidic water from the mines into lakes and streams. Finally, abandoned mines can sometimes simply be filled with sand, gravel, fly ash, or other materials, effectively immobilizing any potential acid-producing substances remaining within them. 

Exposure to formic acid is potentially dangerous. It irritates the skin, eyes, and mucous membranes and may also be toxic to the kidneys. Chronic exposure may lead to kidney damage or dermatitis. Acute exposure produces a variety of symptoms including eye irritation, blisters in the mouth and nasal membranes, headache, nausea, and breathing difficulties. Extreme exposure results in unconsciousness and death. 

Organophosphorus acid extractants have found considerable use in recent years for the recovery of uranium as a byproduct in the manufacture of wet-process phosphoric acid. This acid is obtained by the digestion of phosphate rock with sulfuric acid, and typically contains 0.1 to 0.2 g of uranium per litre.120 It has been estimated that, in 1976, the wet-process acid produced in the USA alone contained some 2500t of dissolved uranium 121 this therefore represents a valuable potential source of this strategic metal. 

In contrast, aspartic acid produces a rather smooth layer (Fig. 11). The fact that a complete recovery of amino acids requires a 6 N HC1 hydrolysis suggests that at least a partial polymerization occurs. Related studies on a number of minerals has indeed shown the polymerization potential of solid state surfaces. Thus, a mineral surface may simultaneously act as a template and a catalyst101,102. ... 

The use of C02 in chemistry normally requires its interaction with metal centers of catalysts one such example is the Kolbe-Schmitt carboxylation of phenol to produce salicylic acid. The potential of C02 as a raw material in the synthesis of carboxylates, carbonates, or carbamates is rather limited. A future aim is the economically attractive synthesis of carboxylic acids, or optically... 

Many industrial organic acids can be produced by fermentation, such as acetic, citric, and lactic acids. Succinic acid is a dicarboxylic acid of potential industrial interest as a platform chemical (1-3). Separation and purification of succinic acid by adsorption was tested to replace current precipitation methods and their associated waste disposal problems. Succinic acid is a valuable intermediate value chemical with a moderate market. For succinic acid to have an economic and energy impact, it will need to become a commodity chemical intermediate with a much lower price. This target price hasbeen estimated to be between 0.22 and 0.30 / lb ( 0.48- 0.66/kg) and is potentially achievable with advanced technology (1). At this price, succinic acid can be catalytically upgraded into other higher valued chemicals suchastetrahydrofuran, 1,4-butanediol, y-butyrolactone, 2-pyrrolidinone, and N-methylpyrrolidinone. 

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