PH modifiers

The principal calcium salt used as a flocculant is calcium hydroxide [1305-62-0] or lime. It has been used in water treatment for centuries (see Calcium compounds). Newer products are more effective, and its use in water and effluent treatment is declining (10). It is still used as a pH modifier and to precipitate metals as insoluble hydroxides. Lime is also sometimes used in combination with polymeric flocculants. 

Leather Taiming. Oxahc acid is used as a pH modifier in leather tanning by tannin and basic chromium sulfate. It also functions as a bleaching agent for leather (qv). 

Phs modified Bodenstein number for solid phase (dimensionless—see just after Eqn. [49])... 

Dissociation of the neutral acid in water necessitates modifications for air-sea exchange in the model, which is based on Henry s law. Other possible pathways, e.g. sea spray, are neglected. Henry s law is restricted to concentrations of physically solved, non dissociated substances. Since only the non-dissociated acid is volatile, it is important to correct the air-water partition coefficient as to reflect the relative proportions of volatile and non-volatile components. The corrected parameter is the effective Henry s law coefficient, which is related to the Henry s law coefficient as a function of pH (modified Henderson-Hasselbalch equation) ... 

HCl was used in the acid pretreatment stage as pH modifier in the ilmenite flotation and cleaning stages. 

Figure 5.4 shows the anodic oxidation of pyrite at different pH modified by CaO and NaOH. Obviously, the oxidation of pyrite is more rapid in CaO solution than in NaOH solution at the same pH. The calcium species in oxidized pyrite surface in the presence of CaO has been identified using XPS as shown in Fig. 5.5. The pyrite surface is oxidized to form Ca(OH)2, CaS04 and Fe(OH)3 in the presence of Ca lime.

With ethyl xanthate (10" mol/L) as a collector, the. flotation recovery of jamesonite and pyrrhotite as a function of pH is presented in Fig. 5.7 with NaOH as pH modifier and in Fig. 5.8 with CaO as pH modifier. It can be seen from these two figures that both jamesonite and pyrrhotite exhibit good flotation response at... 

Figure 5.7 Flotation recovery of jamesonite and pyrrhotite as a function of pH modified with NaOH...

Interfacial Structure of Mineral/Solution in Different pH Modifier Solution... 

Figure 5.10 is EIS of marmatite electrode in O.lmol/L KNO3 solution with different pH modifiers at open circuit potential. This EIS is very complicated. Simple equivalent circuit can be treated as the series of electrochemical reaction resistance R with the capacitance impedance Q == (nFr )/(icR ) resulting fi-om adsorbing action, and then parallel with the capacitance Ca of double electric... 

Figure 10.4 Flotation recovery of galena, sphalerite and pyrite as a function of butyl xanthate concentration with different pH modifiers at pH = 12...

At the same pH made by different pH modifiers, the different flotation response of one sulphide mineral may arise from its effect on the potential of this mineral electrode. The change of potential of mineral electrodes with time at pH= 12 modified by NaOH and Ca(OH)2 is measured and demonstrated in Fig. 10.5. It follows that a mineral electrode potential increases faster with the time at pH= 12 modified by sodium hydroxide and changes a little at the same pH modified by calcium hydroxide. When pH is adjusted by NaOH, the electrode potential of galena, sphalerite and p5oite increase rapidly, respectively, from -30, -12, and 70 mV at the initial stage to -10, 10, and 110 mV after 50 min. When pH is modified by lime, the electrode potential of galena, sphalerite and pyrite... 

Table 10.10 Separation results of the mixtures of two minerals (1 1) among galena, sphalerite and pyrite by h controlled flotation (pH modified by lime, grinding time for 5 min, in Fe medium)...

For the flotation separation of the mixtures of galena-sphalerite, using DDTC as a collector and lime as a pH modifier, the mixture is ground in Fe medium and the potential is made at 90 mV. The lead concentrate assayed of 74.4% Pb and zinc concentrate assayed of 57.51% Zn can be obtained. The recovery of lead and zinc are, respectively, 88.14% and 95.3%. The flotation separation of a mixture of sphalerite mid pyrite is conducted at pH = 12 modified by lime and using butyl xanthate as a collector. The mixture is ground in Fe medium and the potential is 150 mV. The zinc concentrate assayed of 58.1% Zn and sulphur concentrate assayed of 48.56% S can be obtained. The recovery of zinc and sulphur are, respectively, 92.1% and 59.83%. 

A buccal drug delivery system is applied to a specific area on the buccal membrane. Moreover, the delivery system ean be designed to be unidirectional in drug release so that it can be protected from the loeal environment of the oral cavity. It also permits the inclusion of a permeation enhancer/protease inhibitor or pH modifier in the formulation to modulate the membrane or the tablet-mucosal environment at that particular application site. While the irritation is limited to the well-defined area, the systemic toxicity of these enhancers/inhibitors and modifiers can be reduced. The buccal mucosa is well suited for this type of modification as it is less prone to irreversible damage [9]. In the event of drug toxicity, delivery can be terminated promptly by removal of the dosage form. 

Figure 3. TLMs of extrusion texturized pH-modified soy flours (I) pH 9.0 (2) pH 8.0 (3) pH 6.6 (4) pH 5.6 (5) pH 5.3 extruded at LFR (6) pH 5.3 extruded at HFR. Note that alkaline pH could increase the fihrousness of the protein matrix acidic pH produced the opposite effect. P, protein C, insoluble carbohydrate.

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