Academic literature on the topic 'Aqueous complexing agents'

The elements of this group, copper Cu, silver Ag, and gold Au, often called the coinage metals, resemble each other in some ways, particularly their tendency to nobility, but it cannot be said that the properties of Ag are intermediate between those of Cu and Au. Even though the d shell is full, the d electrons are active, particularly in Cu and Au. The most stable oxidation states are II for Cu, I for Ag, and III for Au. For Cu, Cu(I) as the simple ion Cu+ disproportionates in HOH, and Cu(III) is so powerfully oxidizing that it is reduced by HOH. Stability may be brought to Cu(I) and Cu(III) only by complexation or insolubility. For Ag, Ag(II) and Ag(III) are reduced by HOH, stability resulting only by forming complex species or insoluble compounds. For Au, the simple Au+ cation disproportionates in HOH, and Au(II) is not known. a. E–pH diagram. Figure 16.1 sets out the E–pH diagram for Cu at a soluble species concentration of 10−1.0 M. It is assumed that there is no complexing agent or any insoluble compound producing agent other than OH− or HOH. Further, almost all species are being considered in their hydrated forms, that is, the forms that they take in the presence of HOH. Oxidation states of 0, I, and II are present. The reddish-orange Cu is a fairly noble metal, and the sole Cu(I) compound is shown as yellow Cu2O since CuOH is unstable. The Cu+ ion does not appear, even though it has been entered in the construction of the diagram. This reflects its strong tendency to disproportionate into Cu(II) and Cu, as predicted by ΔG˚ values. The compound which results when OH− is added to a blue Cu+2 solution is blue Cu(OH)2, not black CuO. Cu+2 is more properly written as Cu(HOH)6+2, and just off to the left of the Cu+2/Cu(OH)2 line, hydrolyzed species like Cu2(OH)2+2 occur. The legend of the figure shows equations for the lines separating the species.

The elements of this group (zinc Zn, cadmium Cd, mercury Hg) all exhibit a II oxidation state in aqueous systems, and Hg also shows a I oxidation state as indicated by the unusual cation Hg2+2. None of the elements shows oxidation states greater than II, which indicates that the d electrons are not involved. Within the group Zn and Cd resemble each other more closely than Cd and Hg. This is especially evident in the nobility of Hg (E˚ positive for Zn and Cd, negative for Hg), the lack of an Hg hydroxide, the thermal instability of HgO, and the greater stabilities of many Hg complexes as compared to those of Zn and Cd. a. E–pH diagram. Figure 17.1 shows the E–pH diagram for Zn at a 10−1.0 M concentration for soluble species except H+ (and OH−). No complexing agent other than HOH and OH− is assumed to be present. The Zn+2 ion is more properly expressed as Zn(HOH)6+2, and the hydroxo complexes probably have enough HOH attached to realize a coordination number of 6. In aqueous solution, Zn acts only in the oxidation states of 0 and II. The legend of the figure shows equations for the lines separating the species. b. Discovery, occurrence, and extraction. Brass, an alloy of Cu and Zn, dates back to pre-historic times. Indications are that it was produced by heating calamine (ZnCO3) with Cu and C. Pure Zn was being produced in India and China during the thirteenth and fourteenth centuries, and by about 1600, was being imported by Europe. Even before this, some reports indicate that zinc was recognized in Europe, but it was generally believed that it was a mixture of metals. In 1746, Andreas Marggraf published a book describing the production of Zn from its mineral calamine ZnCO3 (now also known as smithsonite), and soon it was recognized by Lavoisier as an element. The name zinc derives from the German zink, which means sharp point, a name designating its appearance when it deposits in a smelter. The major ores of Zn are zinc blende ZnS (also known as sphalerite) and calamine ZnCO3.

For SCR (selective catalytic reduction) applications both aqueous ammonia and urea reagents are used for NOx reducing agents in exhaust systems. For both diesel engines and small boilers, the reagent injection systems often consist of a few, and in some cases, a single injector, located on the wall of the exhaust pipe or duct. Often numerical modeling is performed to determine the location and orientation of the injectors and to predict the NRMS (normalized root mean square) of the gas phase reducing specie distribution prior to the catalyst. Aqueous ammonia and aqueous urea have significantly

Evaporation of High Level and Low Activity (HLW & LAW) radioactive wastes for the purposes of radionuclide separation and volume reduction has been conducted at the Savannah River and Hanford Sites for more than forty years. Additionally, the Savannah River Site (SRS) has used evaporators in preparing HLW for immobilization into a borosilicate glass matrix. The Hanford River Protection Project (RPP) is in the process of building the world’s largest radioactive waste treatment facility, Waste Treatment Plant (WTP), which will use evaporators to concentrate the liquid waste and plant recycle