Iron isoelectric points

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice. 

The Electrical Double Layer and Electrochemical Properties 235 Tab. 10.6 Isoelectric points and points of zero charge of iron oxides. 

These results indicate that the Fusarium lipoxygenase differs from the soybean lipoxygenase in various respects soybean lipoxygenase is a nonheme iron-containing dioxygenase and has a molecular weight of 102,000, optimum pH of 6.5 to 7,0 and isoelectric point of pH 5.4. The soybean enzyme is not inhibited by cyanide and catalyzes the peroxidation of linoleic acid and linolenic acid at equal rates74-76,193. ... 

Silicon, titanium, chromium, and aluminum oxides should be relatively acidic, with isoelectric points near 4.0, 6.0, 7.0, and 7.0, respectively. Iron oxide should be intermediate, with an isoelectric point near 9.0. Parks predicted the isoelectric point of nickel oxide to be of the order of 10-12. Other investigators [20] have reported the isoelectric point of nickel oxide to be near 9.4. 

Ovotransferrin is also obtained from the white portion of a chicken egg and has been used as a chiral selector in liquid chromatography. This protein is also called conalbumin. It is a metal ion (iron, copper, manganese, and zinc) binding protein of molecular mass 70,000-78,000 and with an isoelectric point of 6.1-6.6. This protein is sensitive to acids and heat. 

As further discussed in Chapters 2 and 7, the sorption of arsenic on iron (oxy)(hydr)oxides is very sensitive to pH and competing anions, such as phosphate and sulfate (Goh and Lim, 2004). In general, the sorption of inorganic As(V) decreases as pH values rise from 3 to 10 (Su and Puls, 2001, 1489). H2As04 is the dominant As(V) ion at pH 3-6. At pH <6, the surfaces of iron (oxy)(hydr)oxides usually have net positive charges (i.e. they are below their zero points of charge (ZPCs) and isoelectric points ... 

Size enlargement of fine particles in liquid suspension can be accomplished in a number of ways. Electrolytes can be added to a suspension to cause a reduction in zeta potential and allow colliding particles to cohere. Examples include the use of trivalent aluminum and iron ions to flocculate the particles responsible for the turbidity of many water supplies and the flocculation of metallurgical slimes by pH adjustment to the isoelectric point. Alternatively, polymeric flocculants can be added to suspensions to bridge between the particles. A wide range of such polymeric agents [1] is available today to aid the removal of fine particles from water. 

Ferrozine 3-(2-pyridyl)-5,6-bis(4-phenylsulphonic acid)-1,2,4-triaz-ine (Fig. 4.3) reacts with iron in the iron(II) ferrous state to form an intense pink complex which can be measured spectrophotometrically (lmax = 562 nm). The assay can be performed at pH 1.6 to eliminate interference from turbidity at pH values close to the isoelectric points of proteins which may be present in biological samples under investigation, e.g., serum, and in some instances to decrease interference in the assay from copper (see below). In determinations in which such problems are not considerations, the assay may be carried out at pH 7.4. (This might be more relevant for the assessment of membrane-bound iron under in vivo conditions.)... 

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