Water acidification

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

A mixture of 114.5 g of 5-(3-chloropropylidene)dlbenzo[a i] cyclohepta[1,4] diene, 75 ml of benzene, and about 400 ml of methylamine is heated in an autoclave at 120°Cfor six hours. The excess methylamine is distilled from the reaction mixture under vacuum and the residue is stirred with 300 ml of water. Acidification of the mixture with hydrochloric acid causes the separation of the hydrochloride of 5-(3-methylaminopropylidene)dlbenzo[a,dlcyclo-hepta[ 1,4] diene. The product is collected by filtration and is purified by recrystallizatlon from a mixture of absolute ethanol and ethyl acetate. MP 210°C to 212 C. 

Legislation enacted by both Canada and the United States (see the US-Canada Air Quality Accord, 1991) will, when implemented, reduce the North American emissions of sulphur dioxide by about 50% based upon the 1980 baseline. These projected emission fields have been appplied in the atmospheric source-receptor models that were described above, to provide a projected deposition field for acidic sulphate that would be expected (14). The predicted sulphate deposition fields have then subsequently been appUed in aquatic effects models that provide estimates of regional surface water acidification distributions (50). The regional acidification profiles have then been used in a model of fish species richness (51) that results in an estimate of the expected presence of fish species as compared to that expected in an unacidified case. 

Acidification pollutants, nutrients and chemicals being transported via the atmosphere to alpine regions originate from both nearby and far away sources. Deposition mainly occurs on the land surface where they can lead to soil and subsequent water acidification. Nutrients and chemicals are partly released from soil and land surfaces to water depending on their chemical nature, and on land and soil characteristics (cf. [7, 10], this volume). 

Acid deposition can cause acidification of soils and waters. Acidification can be defined as a reduction of the acid-neutralizing capacity of soils or waters. The acidneutralizing capacity is also known as alkalinity (AUc) and indicates the sensitivity of a water system toward acidification. It can be expressed as [9] ... 

Birks, H. J. B. Juggins, S. Line, J. M. In The Surface Waters Acidification Programme Mason, B. J., Ed. Cambridge University Press Cambridge, United Kingdom, 1990 pp 301-313. 

Belgian workers needed to prepare the benzylidenethiophthalide 1 to test its potential use as a chain-stopper for a particular polymerisation process. 2-Thiophthalide 2 was therefore condensed with benzaldehyde in THF at 0°C using potassium t-butoxide as base. Work-up consisted simply of addition of water, acidification with HC1 and extraction with chloroform. None of the expected product 1 was obtained instead, the stilbene acid 3 was formed in 52% yield. 

Ferrier, R. C., J. D. Miller, T. A. B. Walker, and H. A. Anderson. 1990. Hydrochemical changes associated with vegetation and soils. In The Surface Waters Acidification Programme (B. J. Mason, Ed.). Cambridge Univ. Press, Cambridge, UK. 

Samples are often acidified with a small amount of nitric or hydrochloric acid if to be used for trace metal determinations, and stored in plastic rather than glass vials to minimize the risk of adsorption losses. Storage containers should be acid washed and thoroughly rinsed with deionized water. Acidification may result in precipitation of naturally occurring dissolved organic matter, however. Speciation studies should be completed immediately after collection on fresh samples. 

Though water acidification is one of the most important aspects, one would certainly not expect significant changes in water acidity in all exposed areas. The effect is highly dependent on bedrock geology and the nature of the overburden. No acidification of fresh water is to be expected in areas with appreciable amounts of calcareous rocks. The most well known susceptible areas are those with shallow overburden and quartzbearing bedrock. Acidification can occur in catchments with highly weathered sandy soils with low neutralization capacities. 

Aggrading forests contribute to surface-water acidification in a number of ways. Water discharge decreases because of enhanced evapotran-spiration, causing evaporative concentration of pollutants. Hydrological pathways become modified (Waters and Jenkins, 1992), and coniferous afforestation commonly raises DOC. Dry deposition of acidifying pollutants to a forest canopy increases as the canopy develops. Total deposition of sulfur and other pollutants in throughfall in forests is typically several times higher than bulk deposition outside the forest (Beier et al., 1993 Hansen et al., 1994 Rustad et al., 1994). Episodic acidification caused by marine aerosols... 

Jeffries D., Clair T. A., Dillon P. J., PapineauM., and Stainton M. P. (1995) Trends in surface water acidification at ecological monitoring sites in Southeastern Canada. Water Air Soil Pollut. 85, 577-582. 

NilssonS.l.,MillerH.G.,andMiUerJ.D. (1982) Forest growth as apossible cause of soil and water acidification an examination of the concepts. Oikos 39,40-49. 

Reuss J. O., Cosby B. J., and Wright R. F. (1987) Chemical processes governing soil and water acidification. Nature 329, 27-32. 

Skjelkvale B. L., Stoddard J. L., and Anderson T. (2001a) Trends in surface water acidification in Europe and North America. Water Air Soil Pollut. 130, 787-792. 

S. D Hondt, M.E.Q. Pilson, H. Sigurdsson, A.K. Hanson, and S. Carey, Surface-water acidification and extinction at the Cretaceous-Tertiary boundary. Geology 22, pp. 483-486 (1994). 

Several researchers have investigated the possibilities of membranes for the removal of dispersed water-based ink pigments from wash effluent [121-126]. Generally, membranes, in particular ultrafiltration membranes, have been found to completely remove ink pigments from effluent streams. It has also been observed that the permeate flux and the fouling tendency depend on operational conditions and effluent composition. For instance, coagulation pretreatment [125], feed water acidification [121], and surfactant addition [123] have been found to improve the flux and decrease fouhng. 

Surface water Acidification of sample with HN03 addition of 199Hg oxidization with potassium permanganate solution reduction with sodium borohydride purging to plasma ICP/IDMS ng/L 86-98 Haraldsson et al. 1989... 

Separation of hafnium from zirconium. In a zirconium-hafnium separation process developed by Eldorado Nuclear, a mixture of sodium zir-conate and hafnate can be obtained by fusing zircon sand with NaOH and dissolving the product in water. Acidification with nitric acid then gives aqueous zirconyl (ZrO +, or hydrolyzed Zr + ) and hafnyl (HfO " ") nitrates. Extraction with TBP then gives an extract containing mainly [Hf0(N03)2(TBP) ], but most of the ZrO " " remains in the aqueous phase and can be recovered on evaporation as essentially Hf-free Zr0(N03)2(s). The effectiveness of this process can be ascribed to compounding of factors... 

Discuss the chemistry of natural water acidification and the role of aluminum in these processes. 

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