Particulate iron

Condensate Polishing. Ion exchange can be used to purify or poHsh returned condensate, removing corrosion products that could cause harmful deposits in boilers. Typically, the contaminants in the condensate system are particulate iron and copper. Low levels of other contaminants may enter the system through condenser and pump seal leaks or carryover of boiler water into the steam. Condensate poHshers filter out the particulates and remove soluble contaminants by ion exchange. 

The magnetite film may, under some circumstances, be layered. For example, in power boilers, under conditions of high steaming rate and low steam-water velocity, a secondary film of precipitated particulate iron oxide may form over the original magnetite film. 

Where caustic deposits occur, the resultant corrosion of steel by caustic gouging or stress corrosion cracking (SCC) mechanisms produces particulate iron oxides of hematite and magnetite. It is common to see white rings of deposited sodium hydroxide around the area of iron oxide formation. 

NOTE The development of magnetite needles in the BW should not be confused with the transport by FW of particulate iron, which has its origins in other areas of the boiler system. 

Filtration of suspended solids, primarily particulate iron oxides. Here the preferred media/process is powdered-resin precoat filters. 

Some acrylic acid copolymers are promoted as having a very wide range of functions that permit them to act as calcium phosphate DCAs, barium sulfate antiprecipitants, particulate iron oxides dispersants, and colloidal iron stabilizers. One such popular copolymer is acrylic acid/sulfonic acid (or acrylic acid/ 2-acrylamido-methylpropane sulfonic acid, AA/SA, AA/AMPS). Examples of this chemistry include Acumer 2000 (4,500 MW) 2100 (11,000 MW) Belclene 400, Acrysol QR-1086, TRC -233, and Polycol 43. 

Acrylic acid terpolymers have appeared on the market in recent years. With their broad spectrum of functions, they offer the potential for excellent waterside conditions. In particular, the terpolymers have proved to be very effective particulate iron oxides dispersants and colloidal iron stabilizers. Examples include acrylic acid/sulfonic acid/sodium styrene sulfonate (AA/SA/SSS), such as Good-Rite K781, K797, K798. A further example is acrylic acid/ sulfonic acid/substituted acrylamide (AA/SA/NI), such as Acumer 3100. 

Low iron levels in the feed are essential to avoid damage to the electrode from iron deposition. This is achieved only by correct condensate line corrosion treatment. Polymer dispersants should be fed direct to the feed line and boiler to ensure particulate iron is effectively removed with the BD. 

Iron concentrations are extremely low in these regions (Johnson et al, 1997). The main source is probably particulate iron associated with atmospheric dust (Duce and Tindale,... 

Particulate iron and sulfur oxides, carbonaceous compounds, aliphatic hydrocarbons, chlorides... 

Particulate iron oxides, Typical water flows lOOOgal/t heavy metals, fluorides... 

X 106 Btu Continuous casting, Particulate iron and other water Typical wastewater volume per ... 

Largest sources machine scarfing, hydrochloric acid pickling (acid mists), reheat furnace (NOJ Particulate iron and other oxides... 

Zinc ligands are soluble in neutral and acidic solutions, so that zinc is readily transported in most natural waters (USEPA 1980, 1987), but zinc oxide, the compound most commonly used in industry, has a low solubility in most solvents (Elinder 1986). Zinc mobility in aquatic ecosystems is a function of the composition of suspended and bed sediments, dissolved and particulate iron and manganese concentrations, pH, salinity, concentrations of complexing ligands, and the concentration of zinc (USEPA 1980). In freshwater, zinc is most soluble at low pH and low alkalinity 10 mg Zn/L of solution at pH 6 that declines to 6.5 at pH 7, 0.65 at pH 8, and 0.01 mg/L at pH 9 (Spear 1981). Dissolved zinc rarely exceeds 40 pg/L in Canadian rivers and lakes higher concentrations are usually associated with zinc-enriched ore deposits and anthropogenic activities. Marine... 

Alternative 2 consists of preliminary treatment followed by dual-media pressure filtration, and two-stage air stripping (Figure 8.4). The preliminary treatment step for iron removal would be exactly the same as specified under Alternative 1. The filters would be recommended to remove suspended matter and particulate iron prior to the air strippers. The required filtration capacity could be provided with either a duplex system of two 60-in.-diameter filters or a triplex system of three 42-in-diameter filters. 

To return to our case study of iron, the equilibrium concentration of Fe(III) is ultimately controlled by its mineral solubility. Since atmospheric dust is a major source of new iron to the ocean, its solubility is a matter of hot debate. If the solubility is low, the particulate iron is likely to settle out of the euphotic zone before it can be assimilated by plankton. Iron is one of the most abundant elements in Earth s crust, so it is not surprising that concentrations in dust are high, ranging from 3 to 5% dry weight. 

Although the details of the equilibrium model are still uncertain, the general trends are likely reliable. As shown in Figme 5.16, most of the Fe(III) in seawater is predicted to be in the form of the FeL complex. The equilibrium model also predicts that this degree of complexation should enhance iron solubility such that 10 to 50% of the iron delivered to the ocean as dust will eventually become dissolved if equilibrimn is attained. If this model is a reasonable representation for iron speciation in seawater, uptake of [Fe(III)]jQjgj by phytoplankton should induce a spontaneous dissolution of additional particulate iron so as to drive the dissolved iron concentrations back toward their equilibrium values. 

The data presented in Table 11.1 indicate that the fluvial gross river flux is the major source of trace metals to the oceans and that most of this flux is in particulate form (fluvial gross particulate flux). But the majority of this particulate flux is trapped within estuaries, primarily via settling, and, hence, is not released into the open ocean. As a result, the fluvial net particulate flux is only about 10% of the fluvial gross particulate flux. In seawater, most of this particulate metal remains in solid form due to low solubilities. The particulate metals eventually settle to the seafloor and are subsequently buried in the sediments. In the case of iron, a small fraction of the particulate pool does dissolve. In the surface waters, solubilization of particulate iron can provide a significant amount of this micronutrient to the phytoplankton. 

The particulate iron(ni) maximum is deeper than that of the particulate Mn maximum. This reflects the lower energy yield of iron respiration and its fester rate of... 

The oxidation-reduction potentials and reaction constants of oxidation of iron and manganese differ and these reactions can occur in different amounts of oxygen. That is why the level of appearance of particulate manganese is situated higher than that of particulate iron [63]. Bacteria have been shown to oxidize manganese [64], whereas iron oxidation is possible without bacteria but can be carried out with bacteria [50]. Reduced iron can be oxidized by particulate manganese, forming complex compounds [65]. 

The maximum in the vertical distribution of Fe(III) (a = 15.8-16.3 kg m 3) is characterized by smaller values—usually less than tens of nM [68] reaching 0.3 pM as maximum [72], Our data for the northeastern (January, July 2004) and southwestern (March-April 2003) Black Sea showed the following. The profile of Fe(III) was characterized by two maxima with values reaching about 100-150 nM at 150 m (erg = 15.8-15.9 kgnr3) and 170-175 m (or = 16.0-16.25 kg m 3). Sometimes a third maximum is observed shallower at 120 m (a-0 = 15.35-15.40 kgm-3). These maxima are correlated with layers of high contents of particulate iron and could be present as colloidal iron goes through the filters (0.45 pm) and is measured as dissolved iron. 

As indicated in Fig. 1, light may induce the reduction of Fe(III) present as particulate iron oxides and oxyhydroxides (Processes 13 and 14). The resulting Fe(II) species could induce the formation of a mixed valence oxide at the particle surface or, more hkely, be released to solution resulting in dissolution of the solid phase. Whether the ferrous iron remains in solution or oxidises and reprecipitates as a ferric oxyhydroxide will be dependent particularly upon solution pH. If other species are adsorbed to the oxide surface, they may also undergo redox transformation as a result of reduction of the metal centre. Such photo-transformations are described in this section. 

The possibility of using particulate iron oxides to induce contaminant degradation has resulted in a variety of studies into the possibility of at-... 

The use of particulate iron precipitant such as sponge iron gives a relatively faster copper precipitation rate than scrap iron of varying sizes. Back (Bl, B2) reported the development of an inverted cone type pre-... 

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