The basic principle of special flotation (2)
It can be seen from the above formula that the parameters affecting the adsorption amount of the target ion in the electric double layer of the gas-liquid interface are concentration C, ion valence z and potential Ψ T . When other anti-ion ions are present in the solution, they will compete with the target ions to interfere with the sorting of the target ions. For example, ion flotation of Sr 2+ can be achieved with sodium alkylbenzene sulfonate, but when the Na + content in the system is too high (Na + /Sr 2+ >10 3 ), ion flotation of Sr 2+ cannot be performed. It can be seen that the electrostatically charged trapping effect is very poor and is susceptible to interference with ions of the same name as the target ion. This sorting process by complex chelation or hydrophobic precipitation has better selectivity. Wherein C—the solubility of M m A n in terms of molarity; Wherein C ' A - excess A m - ion molar concentration; Where a M , a A —- participate in the side reaction coefficient of the side reaction component; Where K w — the ion product of water; Woven Fabric Cutting,Factory Fabric Cutting Machine,Fabric Cutting Equipment,CNC Fabric Cutting Machine Jinan Zhuoxing Intelligent Technology Co., Ltd. , https://www.zhuoxingcutter.com
The ion flotation selectivity by the surfactant to the foam layer by the hydrogen bonding force and other intermolecular bonding forces is also poor.
and b complexation or chelation complex (or chelate) hydrophobic collector formed precipitate the heavy metal ions, whether soluble or water-insoluble precipitate, since the non-polar vigor, a polar group, and The metal ions combined are oriented toward water and thus have surface activity (hydrophobicity), which is easy to adsorb or adhere on the bubbles, forming a three-phase foam composed of liquid-gas two-phase foam or a crystal or precipitate and water and gas phase. Or floating film (Figure 3b above).
Alkyl xanthate, alkyl and aryl ammonia sulphate, alkyl thiol, diphenyl sulfonium, butyl hydrazine, test copper , a-furyl hydrazine, phenyl-a-pyridyl ketoxime, A-nitroso-β-naphthol, β-nitroso-a-naphthol, 8-hydroxyquinoline, benzoylacetone, etc. form precipitates with most non-ferrous metals, rare metals, noble metal ions, such precipitates It is hydrophobic and is directly enriched in foam (Figure 3c above). This is the so-called class II precipitation flotation. For example, flotation of ions with a nickel reagent:
(2) Precipitation flotation
Precipitation flotation is the stoichiometric addition of the required precipitant to the system, so that the target material is completely converted into a precipitate, and a surfactant is added to cover a part of the surface of the particle so as to adhere to the bubble or to precipitate bubbles on the hydrophobic surface thereof. The key to the success of sedimentation flotation is the degree of conversion of the target to the precipitation and the flotation behavior of the sediment. [next]
When the removal or recovery of metal ions in aqueous solution, most of the precipitate to form a hydroxide or sulfide, may also be employed in the form of carbonate or phosphate precipitates.
A Calculation of solubility of poorly soluble substances The formation and dissolution of precipitates of poorly soluble substances conform to the solubility product rule. The solubility product can be used to estimate whether the precipitation is complete (it is generally considered that the content is less than 10 -5 moles - liter -1 is complete precipitation). However, most of the complexes encountered in the sediment flotation are multi-component mixed systems, and the influence of various factors on the solubility must be considered. In general, the common ion effect reduces the solubility of poorly soluble substances; the inert electrolyte increases the solubility of poorly soluble substances, but when the ionic strength I is greater than 4, the solubility decreases, and side reactions (metal ion hydrolysis, proton transfer reaction, network) The combined reaction and redox reaction generally increase the solubility of the poorly soluble substance.
The solubility of a M m A n in pure water The precipitation equilibrium of the material composition of M m A n is:
M m A n ===mM n+ +nA m-
The solubility product is: K s =[M] m [A] n =( mC ) m (nC) n (2)
Solubility is:
K s ——— Thermodynamic solubility product constant of M m A n ;
[M], [A] - the activity of the component, when the concentration is very low, the concentration can be used instead.
b M m A n solubility in the same ion solution If the substance M m A n is dissolved in a solution containing excess A m- ions, the excess A m- ion concentration is C ' A and C ' A Nc, then MmAn The solubility C is:
C—the solubility of M m A n in an inert electrolyte solution.
In the inert electrolyte solution, the ionic activity of the precipitate is reduced due to an increase in the ionic strength, thereby causing an increase in the actual solubility of the poorly soluble substance. The effect of the change in ionic strength on the ion activity coefficient of the precipitate formed can be calculated by the Debye-Huckel equation. The precipitation of high-valent ions is greatly affected by the ionic strength.
The solubility at a certain ionic strength can usually be calculated from the thermodynamic solubility product and the activity coefficient at the corresponding ionic strength value of the insoluble salt. [next]
C Solubility in systems with side reactions If a component of the poorly soluble compound M m A n participates in a side reaction, the solubility of the material will increase. When calculating the solubility, the thermodynamic solubility product K s in the formula (3) or the formula (4) is replaced with the conditional solubility product K s * (the formula (4) is used when the common ion excess of the precipitant is present.
The conditional solubility product K s * is calculated from the thermodynamic solubility product and the side reaction coefficients a m and a A in which the components participate in the related side reactions.
a M =[M]'/[M]
a A =[A]'/[A]
[M] and [A]—the equilibrium concentration of free ions;
[M] ' and [A] ' -- the total concentration of all forms containing M or A in the solution;
K s — The precipitation reaction, that is, the thermodynamic solubility product of the main reaction.
d Solubility of hydroxides For poorly soluble hydroxides, the effect of side reactions of hydroxy complex formation on solubility must be considered. Thus, various insoluble metal hydroxides have their own optimum precipitation pH ranges. At a certain pH, the solubility of hydroxide M(OH) n is:
K s * ——— The conditional solubility product of M(OH) n .