Precipitations with Other Metals

Problem With the help of the previous experiments, further suppositions occur as to which metals react with which metal salt solutions. They can be tested in test tubes afterwards the metals are arranged in the well-known metal activity sequence. 

Material Test tubes various metal strips or wires, appropriate salt solutions. Procedure Dip the metal pieces systematically into different salt solutions and test for reactions. Record positive reactions in tabular form. 

Observation Relative noble metals like copper, nickel and lead are deposited from their solutions in the presence of active metals like magnesium, zinc or iron. 

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The solubilities of some heavy metal sulfides are extremely low, so precipitation by H2S or other sulfides (see Reaction 22.5.2) can be a very effective means of treatment. Hydrogen sulfide is a toxic gas that is itself considered to be a hazardous waste (U135). Iron(II) sulfide (ferrous sulfide) can be used as a safe source of sulfide ion to produce sulfide precipitates with other metals that are less soluble than FeS. However, toxic H2S can be produced when metal sulfide wastes contact acid ... 

Approximately 80% of Zn production involves hydrometallurgy, in which roasted sulfide concentrates are dissolved in sulfuric acid.181 Currently, the major separation steps involve the precipitation of other metals from the sulfate stream (Figure 7) 181>182 The precipitation of iron is achieved by raising the pH with calcine, the mixture of zinc/iron oxides from roasting, producing large volumes of iron oxy-hydroxide materials, the disposal of which presents major challenges.183-185... 

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

This precipitate dissolves in thiosulphate to form a thiosulphate complex, which, in common with other metal thiosulphate complexes, decomposes when heated to the metal snlphide (see Sec. 3.3.3). Besides direct decomposition of the thiosnlphate complex, another possibility suggested in this study is formation of snlphide ion by alkaline hydrolysis of thiosulphate [Eqs. (3.20) to (3.24)] and reaction with Hg to form HgS. The substrates were glass precoated with a very thin film of CD PbS (presnmably this improved adherence and/or homogeneity). 

The ferrous ion is a reducing agent, therefore, ferrous sulfate or ferrous chloride coprecipitation method can reduce hexavalent chromium to the trivalent state and subsequently precipitate it along with other metals. 

Precipitation Sequence. It should be concluded that the ions from the more noble metals are changed into atoms and crystallized from the solution. Simultaneously, due to electron transfer, the atoms of the active metal go into solution through the formation of ions. This hypothesis can systematically be tested with other metal pairs (see E8.4) the observations are noted by the precipitation sequence of the metals. 

For pH valnes above 8, precipitate flotation was more efficient in removing zinc than foam separation of soluble zinc species.15 The optimum pH was 9.2. The surfactant was SDS. The adsorbing colloid flotation of zinc used aluminum hydroxide and NLS in the pH range 8.0-8.6 ferric hydroxide floes were not effective. Removal was 99.8% or higher.15 Table 17.3-1 shows the removal of ziec in association with other metals. 

Recovery of uranium from leach liquors. Uranium may be recovered from leach liquors by precipitation, ion exchange, or solvent extraction. Precipitation with sodium hydroxide was the recovery method used in the first uranium mills. When used on sodium carbonate leach liquors, the uranium precipitate is fairly free of other metallic contaminants, because sodium carbonate dissolves few other metals beside uranium. However, when used in sulfuric acid leach liquors, the uranium precipitate contains other metals, such as iron dissolved from the ore by the add, and is no longer commercially acceptable. Consequently, in the United States, uranium mills emfdoying add leaching now follow it with selective recovery by either solvent extraction or ion exchange. These processes are described in Secs. 8.5 and 8.6, respectively. 

A number of anions form slightly soluble precipitates with certain metal ions and can be titrated with the metal solutions for example, chloride can be titrated with silver ion and sulfate with barium ion. The precipitation equilibrium may be affected by pH or by the presence of complexing agents. The anion of the precipitate may be derived from a weak acid and therefore combine with protons in acid solution to cause the precipitate to dissolve. On the other hand, the metal ion may complex with a ligand (the complexing agent) to shift the equilibrium toward dissolution. Silver ion will complex with ammonia and cause silver chloride to dissolve. 

Absorption-precipitation. Many agents may form a larger complex - precipitates with other particles such as metallic ions (aluminum, bismuth, calcium, iron)-while passing via the gastrointestinal tract. 

One single property of micelles is more important than any other they solubilize organic compounds in water. A single sodium dodecyl sulfate (SDS) micelle, for example, dissolves up to 40 benzene molecules or a single porphyrin molecule or one hydrophobized AT pair (Fig. 2.5.4). Very often micelles made of long-chain sulfonates are chosen as solubilizers instead of the natural carboxy-lates, because carboxylates tend to precipitate with bivalent metal and ammonium counterions. Sulfonate micelles are much more hydrated and remain, for... 

Under physiological conditions, as well for trace analytical procedures, no precipitations are considered coprecipitations, however, can be used for analytical separations (Sager, 1986 Sager, 1992). In the system Tl-S, 8 different phases are known besides mixed sulfides with other metals (Fialkov and Muzyka, 1952). TI2S can add elemental sulfur as well as polysulfide, which lowers its solubility, in open air, on the other hand, TI2S is easily oxidized to soluble TI2SO4. Monovalent thallium forms stable com-... 

Molybdenum is released from rocks by the processes of weathering (Mitchell, 1964), which involve one or more cycles of solution, oxidation, and precipitation before the Mo from a given rock either appears in the soil formed from that rock or is transported to ocean sediments as part of the sedimentary cycle. Molybdenum is fairly readily released from primary minerals by weathering, and, as compared with other metals, it remains relatively mobile as potentially soluble molybdates (Mo +). Consequently, transport of Mo via leaching is likely unless iron, aluminum, or manganese oxides interfere under conditions appropriate for occlusion by those minerals (Davies, 1956). 

To test the ability of Fe(IIl) to compete for DMA with other metals, two-metal scenarios were modeled. The findings from this suggest that while Fe(III) is able to effectively compete with Zn, Cd, Cu or Ni at low pH and complex the majority of the DMA present, at higher pHs, the other metals predominate DMA complexation (see Fig. 3). Further GEOCHEM-PC simulations with 25 tiM concentrations of DMA, Fe(III), and Cd/Zn/Cu/Ni, and with neither precipitation nor mythical soil ligand, were of the same general shape as those in Fig. 1 but had... 

Modern shampoos are simple surfactants, such as sodium lauryl sulfate and sodium dodecyl sulfate. Shampoo contains other ingredients, however, that react with the meted ions in hard water to help prevent the soap from precipitating with these metal ions (in other words, to help prevent insoluble precipitates — solids, deposits, bathtub ring — from forming in your hair). 

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