The low solubility of reagents in water (flotation pulp) causes technical and technological complications (high reagent consumptions, necessity for preheating the pulp and emulsifying the reagent, its effect on froth formarion, etc.).The form in which the reagent is introduced imo the pulp has an important effect on its reaction with the mineral particles, which largely determines the results of the flotation process as a whole. The solubility of the reagent in water may be markedly changed by a cor~roUed change in its flotation properties by introducing cha.,'-acteristic atomic groups and various sub~ituer~ [I, 2]. Thusthe factom governing the solubility of a reagent in water, and methods for increasing the solubiUty of reagents, are of practical interest for flotation.Water is a high-polar solvent which is highly associated owing to formation of hydrogen bonds (H bonds) between its molecules. Organic substances the molecules of which are relatively small such as ethers, aldehydes, amines, carboxylic acids and ketones, dissolve in water largely owing to formation of H bonds [3,4]. The electronegative atoms between which H bonds are formed are usually oxygen, nitrogen, or fluorine, and in certain cases chlorine. This relates to syltems in which the presence of H bonds is well known.However, it is assumed that the condition of high eleotronegativity of the atoms is not obligatory for formation of a hydrogen bond [3]. Acids which form H bonds include halogen--activated C-H groups, acetylene groups C = H, and SH groups (haingen=sub~itnted thiophenols dithiophosphoric acids [5], etc.).Proof of the capacity of the sulfur atom to act as a base for formation of an H bond has been obtained for ethylene thiourea Nitrogen forms'hydrogen bonds only slightly weaker than oxygen bonds. Sulfur is far less effective in hydrogen-bond formation than oxygen; therefore,replacement of O by S in compounds of similar structure always greatly reduces their solubility in water. Thus the solubility (t = 20~ of urea is 108.3 g per 100 g of water, while that of thiourea is only 12.0 g [11].Aliphatic hydrocarbon chains and aromatic rings which cannot participate in such reations reduce the solubility of the substance in wate~ this effect being intensified with increasing lengthening of the chain or with in = troduction of a greater number of rings, As shown by Kakovskii ['12], the solubillty of a reagent in water is reduced by a factor of 4,3 with an increase in its length by one hydrocarbon chain (within the same homologous series). P~placement of the hydrogen atoms of aromatic rings by halogen atoms or nitro groups Sways reduces the solubility of a reagent in water. This must be borne in mind because in a number of cases the selectivity of a reagent may be heightened by introducing halogen atoms or nitro groups into its molecule without changing the length of its hydrocarbon radical (the number of aromatic tings).The solubility of an organic reagent in water may be increased in two ways.Giredmet, Moscow.
The simplest approximations (one-dimensional reactor, single-group diffusion model of neutron transfer) are used to study the characteristics of xenon oscillations in a reactor with negative feedback on the coolant temperature. It is shown that in this case, in contrast to the situation where the predominant feedback is on the neutron fl ux density, the emergence into the xenon instability regime will manifest in the form of perturbations of the reactor power and energy release simultaneously. In addition, the deformations of the energy-release fi eld grow with increasing neutron fl ux and physical dimensions of the reactor.Theoretically, in the absence of external control the principal harmonic of the energy-release fi eld is least stable against xenon oscillations, while the higher-order harmonics are less subject to them [1]. An important circumstance is that this result was obtained for negative feedback on the neutron fl ux density. We shall consider a different situation where feedback is determined by the coolant temperature, which is a characteristic situation when, for example, high-enrichment uranium is used.We shall use a qualitative physical model similar to that in [1]. We shall study a planar reactor surrounded by an ideal refl ector; the neutron fl ux will be described in a single-group diffusion approximation, neglecting the delay in the emission of delayed neutrons and the lag in the manifestation of feedback. This model corresponds to the system of equations:where the generally accepted notation is used, and for brevity the arguments of the indicated functions are omitted. With the exception of k(z), we shall assume the parameters appearing in the equations to be constants. Let us consider a stationary state of the reactor with the neutron fl ux being independent of the spatial coordinate: Φ(z, t) = Φ 0 . In this case, the concentration of iodine and xenon also becomes constant I(z, t) = I 0 and X(z, t) = I 0 , which can
Despite the extensive use of chelate-forming reagents, flotation specialists have not yet obtained definite information on the composition and structure of the surface compounds formed during adsorption of the reagents on minerals. However, this theoretical problem has now become of great practical importance in connection with the development of the principles of direct selection and synthesis of flotation reagents with given properties.To develop selective flotation reagents, we can put to good use the experience gained in the neighboring regions of use of chelate-forming reagents (extraction, precipitation, etc.). Such an approach is based on the assumption that the laws of formation of the chelate ring during the reaction of chelate-forming reagents with metals in a solution and with mineral surfaces are the same [i]. Direct proof of this would give a sound theoretical basis for the postulated and present-day principles of selective flotation reagent selection [2, 3].Research by Solozhenkin [4, 5] is therefore of great interest; using the ESR method he investigated the structure of the products of reaction of sulfhydryl reagents with the surfaces of nonferrous metal sulfides.In particular, he established that when particles of Cu(ll)-activated chalcopyrite and other sulfides are previously floated with sodium diethyldithiocarbaminate (Na-DEDC), copper (II) bis-(dlethyldithiocarbaminate) passes into the solvent: S IS
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