Calcium arsenates concentration

The local formulator who purchases concentrated products from the manufacturer has his problems. More frequently than not the advent of a new product catches him with a stock of some older chemical which the new one will replace. Lead and calcium arsenates, rotenone, pyrethrum, sabadilla, and others all have lost some usage to the newer economic poisons. Costs such as these cannot be passed on to consumers because of that grand American institution, competition. 

Additionally, both calcium arsenate and ferrihydrite approached equilibrium with increased depth in each borehole, which was well correlated to the observed increased As aqueous concentrations. 

Geochemical modeling is often used to identify the compounds that primarily control the chemistry of arsenic in aqueous solutions. Modeling studies indicate that the arsenic concentrations of Kelly Lake, Ontario, Canada, are controlled by the precipitation and dissolution of Fe(II) arsenates rather than calcium or Fe(III) arsenates (Sadiq et al., 2002). The arsenic in the lake originated from runoff from the nearby Sudbury mining district and airborne particles from local ore smelters (Sadiq et al., 2002). 

With the lowering of the US arsenic drinking water standard (MCL) from 50 to 10 pg L-1 (Appendix E), water treatment facilities may have had to modify their procedures to comply with the new standard. Boccelli, Small and Dzombak (2005) identifies some of the factors associated with Fe(III) chloride coprecipitation that might require modification while still maintaining reasonable costs. Besides the influent arsenic concentration and Fe(III) chloride dose, other critical factors in improving arsenic removal may include pH, the calcium and major anion concentrations of the influent, the volume of sludge, equilibrium sorption constants, and filter efficiency. 

Cupric arsenate, Cu3(As04)2.—The arsenate occurs as pentahydrate under the name trichalcite. The tetrdhydrate is produced by heating cupric nitrate with calcium arsenate, or copper with a solution of arsenic acid,1 and also by the interaction of cupric chloride and silver arsenate.2 Concentration at 70° C. of a solution of cupric carbonate in excess of arsenic acid yields pale-blue leaflets of the formula CuHAsO 4,H20.3 Other acidic salts,4 and also basic salts,5 are known. 

In wines, traces of iron, which are picked up, perhaps, from processing and/or storage, or copper, which are picked up from mildew sprays, such as Bordeaux mixture, affect the oxidative stability of wines by acting as the redox shuttles as they transfer between oxidation states. Winemakers discovered that adding ferricyanide to wine, in a process known as blue fining, precipitates copper and iron and thereby reduces their concentrations below 1 ppm, which is considered to be acceptable. Critical control of ferricyanide addition is necessary, as cyanide is also a contaminant that must be measured. Where vineyards have replaced cherry and apple orchards, low concentrations of arsenic have started to appear but they are present at very low concentrations in high quality wines. The arsenic appears from arsenical compounds such as lead and calcium arsenates that were used for many decades as pesticides on apples and cherry orchards. 

In situ metal immobilization employing phosphate is a cost-effective and environmental friendly technique of less disruptive nature [24, 28, 47, 76] than other remediation techniques such as soil removal, washing or leaching. This technique was suggested by the United States Environmental Protection Agency in 1996 as an alternative to soil removal for the amendment of urban lead-contaminated soils [27]. The treatment of waters with calcium oxide or hydroxide can precipitate dissolved arsenate. To attain a total dissolved arsenic level lower than the maximum permissible concentration for total arsenic in potable water (0.010 mg/L arsenic) it is necessary to have a pH higher than 12.5, which poses other environmental problems. Under these conditions calcium carbonate wiU be the thermodynamically stable solid phase under ambient surface conditions. Transformation of calcium arsenates into calcium carbonate wiU re-release arsenic into the environment. For pH > 12... 

Extensive studies have shown that arsenic can accumulate in the soil when arsenic compounds are repeatedly applied to crops [1]. On fields treated with calcium arsenate for insect control, the arsenic concentrations decreased with soil depth [1]. Appreciable amounts of arsenic could also move down in the soil profile with the percolating soil water [13]. 

Arsenates are oxidizing agents and are reduced by concentrated hydrochloric acid or sulfur dioxide. Treatment of a solution of orthoarsenate with silver nitrate in neutral solution results in the formation of a chocolate-brown precipitate of silver orthoarsenate, Ag AsO, which may be used as a test to distinguish arsenates from phosphates. With hydrofluoric acid, orthoarsenate solutions yield hexafluoroarsenates, eg, potassium hexafluoroarsenate [17029-22-0] (KAsFg)2 H2O. Arsenates of calcium or lead are used as insecticides sodium arsenate is used in printing inks and as a mordant. 

It may be necessary to segregate waste streams containing elevated concentrations of arsenic and selenium, especially waste streams with concentrations in excess of lmg/L for these pollutants. Arsenic and selenium form anionic acids in solution (most other metals act as cations) and require special preliminary treatment prior to conventional metals treatment. Lime, a source of calcium ions, is effective in reducing arsenic and selenium concentrations when the initial concentration is below lmg/L. However, preliminary treatment with sodium sulfide at a low pH (i.e., 1-3) may be required for waste streams with concentrations in excess of lmg/L.22 The sulfide reacts with the anionic acids to form insoluble sulfides that are readily separated by means of filtration. 

The concentrates were subsequently analysed for arsenic using Varian-Techtron AAS atomic absorption spectrophotometer fitted with a Perkin-Elmer HGA 72 carbon furnace, linked to a zinc reductor column for the generation of arsine (Fig. 5.3). A continuous stream of argon was allowed to flow with the column connected into the inert gas line between the HGA 72 control unit and the inlet to the furnace. Calcium sulfate (10-20 mesh) was used as an adsorbent to prevent water vapour entering the carbon furnace. The carbon tube was of 10 mm id and had a single centrally located inlet hole. 

Liquid MD penetrates skin on contact. Prolonged skin exposure to its arsenic component will lead to systemic damage through bone calcium displacement and subsequent bone marrow destruction. In its traditional form, MD quickly disperses in open terrain but presents a more prolonged hazard in tightly closed buildings, where it concentrates in basements and substructures due to its vapor density.1... 

Admixture incompatibilities - Magnesium sulfate in solution may result in a precipitate formation when mixed with solutions containing Alcohol (in high concentrations) alkali carbonates and bicarbonates alkali hydroxides arsenates barium calcium clindamycin phosphate heavy metals hydrocortisone sodium succinate phosphates polymyxin B sulfate procaine hydrochloride salicylates strontium tartrates. 

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