Janusz Lekki

Surface dissociation constants for solid oxide/aqueous solution systems

SummaryAn equation for the surface potential ψ0 was used to define the surface dissociation constant of surface hydroxyls at a solid oxide/aqueous solution interface.Using the measurements of the surface charge, the Gouy-Chapman theory and crystallo-chemical data for oxides, the calculations of the surface dissociation constants have been carried out. The values of the acidic surface dissociation constants (in minus logarithmic scale) fall in range 8.7±0.8 at ionic strength 1 M and in the range 7.2±0.7 at 10−3 M KNO3 These constants exceed by 2 to 5 orders of magnitude the dissociation constants of M(OH)naq species in solution.

Flotometric analysis of the collectorless flotation of sulphide materials

Abstract Collectorless flotation of different size fractions of sulphides and sulphur was conducted in a monobubble-type Hallimond tube. Flotation tests were carried out with sulphides of different origins at their natural pH and natural redox potential in distilled water. The floatabilities of sulphides were compared to the floatabilities of hydrophobic elemental sulphur and hydrophilic quartz and magnetite, taking into account the density of the investigated solids. It was established that chalcopyrite, pyrite, galena and copper (I) sulphide floated as well, or almost as well, as elemental sulphur. This indicated the presence of sulphur or a layer of sulphur-excess sulphide on the surface of these solids during flotation. The floatability of another galena and another pyrite, sphalerite, iron (II) sulphide and nickel (II) sulphide was found to be equal, or almost equal, to the mechanical carry-over of hydrophilic quartz and magnetite, most likely because of hydrophilicity of a fresh sulphide surface or the presence of such hydrophilic products as metal hydroxides or metal sulphuroxy compounds. It was also suggested that the so-called parameter L of the “flotometric equation” can be used to characterize the flotation properties of sulphides. The flotometric equation has the form a 50 ϱ′ = L 50 , where a 50 is the maximum diameter of the particle which can be successfully floated, while ϱ′ is the density of the solid in water.

Flotometry—Another way of characterizing flotation

On the basis of various flotation tests with quartz and magnetite a new method of evaluating flotation processes is described. The proposed method, called flotometry, relies on carrying out a series of flotation (recovery, R, vs time, t) tests using increasing particle size until the particles become too heavy to be floated. The flotation tests are conducted with a monobubble-type Hallimond tube and analyzed with the flotometry equation in the form aR,t,sρ′ = LR,t,s′, where aR,t,s is the size fraction of the solid for which recovery is R after time t of flotation, s denotes surface properties of the solid in the flotation system, and ρ′ and LR,t,s represent particle density in water and a constant, respectively. Flotometry seems to be a useful method for determining the type of flotation, solid hydrophobicity in the flotation solution, upper critical particle size for flotation, strength of the solid-bubble contact, and other factors in flotation systems.

Mechanical, contactless, and collector flotation in the hallimond tube

Abstract Different size fractions of quartz or magnetite were floated separately in a Hallimond tube. Recovery vs flotation time results and contact angle measurements showed that the following types of flotation took place, depending on conditions: mechanical carryover in pure water, contactless flotation in aqueous ethyl alcohol, and collector flotation in the presence of 10−3 M aqueous dodecyl amine for quartz or 10−3 M aqueous sodium oleate for magnetite. It was established that the maximum size of a particle which can be floated in the Hallimond tube depends on the type of flotation and the density of the solid. The maximum particle size which can be transported from the main body of the Hallimond tube to the product receiver increases in the order mechanical carryover, contactless flotation, collector flotation. It was also found that for all three kinds of flotation the quartz particle diameter to magnetite particle diameter ratio is equal to 2.6 ± 0.2, if comparison is made with the same recovery, time of flotation, and hydrophobicity. This indicates that the hydrodynamics of particles floated in a Hallimond tube, producing a single train of monodispersed bubbles at a gas flow rate of 0.625 cm3/s, follows Netwons law for a turbulent liquid medium.

A study of the germanium-sodium oleate flotation system

Abstract The results of germanium flotation in 0.0001 mol/l sodium oleate aqueous solutions are presented. Zeta potential data and the results of IR spectrophotometric measurement suggest that flotation in the pH range from 0 to 4.5 is due to physical sorption of liquid oleic acid on to the naturally hydrophobic surface of germanium, whereas flotation in the pH range from 4.5 to 10 is caused by physisorbed layers of oleate species, consisting of oleic acid and sodium oleate.

DYNAMIC INTERACTION IN PARTICLE - BUBBLE ATTACHMENT IN FLOTATION

ABSTRACT The capture of a bubble is discussed with particular emphasis placed upon the stability of the disjoining film between a bubble and a particle. The thermodynamic criterion of flotation, θ>o, must be fulfilled for flotation to be possible, but at the same time the kinetic criterion must be met also. Frothers do not usually affect the contact angle but they speed up all processes in the system and influence the rate of flotation. The natural floatability of chalcocite was shown to be maximal at pHs close to the IEPs for CuS 2 O 3 and Cu(OH) 2 , that is, at the IEPs of oxidation products on the surface of chalcocite. The effect of frothers was very noticeably far from these values of pH. It is known that to describe the stabilization of hydrophobic dispersions by nonionic surfactants, that is the change from the very hydrophobic state to the very hydrophilic one, an introduction of the entropic term, ΔG s , into the general equation was necessary. In the flotation case covering the full range of changes from very hydrophilic to very hydrophobic, the same parameter is necessary to describe the properties of the system. Calculations have shown that the particle-bubble interaction under conditions of constant surface charge leads to an increase in surface potential. This change is high enough to cause desorption of physically adsorbed frother from a solid at the moment of collision with a bubble. Diffusion of large organic molecules across the hydration layer at the very moment of attachment disorientates this layer lowering the value of ΔG s .

The effect of contact of copper sulphide grains on the initial rate of leaching in oxygenated sulphuric acid solution

Abstract The initial stage of leaching of chalcocite, bornite, and chalcopyrite as well as chalcocite-chalcopyrite and bornite-chalcopyrite mixtures in oxygenated aqueous sulphuric acid was investigated at 368 K. It was determined that chalcopyrite accelerates the rate of copper leaching from chalcocite due to grain contact between chalcocite and chalcopyrite. In contrast, chalcopyrite decreases the rate of dissolution of bornite.

Application of flotometry for characterizing flotation in the presence of particles aggregation

Abstract Different size fractions of coarse magnetite were floated in water in a monobubble Hallimond tube with an increasing dosage of sodium oleate (Na01), diethyl dixanthate ((EtX) 2 ), and hexadecane. All maximum recovery (R m ) vs collector concentration curves plotted for various size fractions were similar in shape having zero recovery at a low and high collector concentration with a maximum recovery in between at a characteristic collector dosage c m , which provides maximum hydrophobicity of the system. Properties of the studied flotation system and literature data indicated that the cessation of magnetite flotation with a high dosage of Na01 is due to hydrophilic layers of oleate ions sorption, while in the other two systems it is due to oil agglomeration of the solids. The values of the maximum particle size which can still be floated (a m 50 ), taken from the maximum recovery vs particle mean size at the concentration equal to c m and R m =50%, seems to be the parameter which well characterizes any solid-collector-water flotation system because this value derives mainly from the hydrophobic properties of the flotation system and particle density in water, ϱ ′ . The a m 50 value and the so-called “flotometry equation” (for our Hallimond tube in the form L m = a m 50 ϱ ′ ) were used for calculation of the parameter L m which in turn was used for a comparison of the floatability of magnetite with different collectors and subsequently with other flotation systems. The values of parameter L m indicated that magnetite floatability increases in the order: collectorless (mechanical carryover), flotation with (EtX) 2 , flotation in the presence of hexadecane, and oleate flotation. It was established that the floatability of magnetite with Na01 is equal to the floatability of galena with (EtX) 2 and very similar to the collectorless floatability of Teflon. Floatability of the above three systems is most likely the maximum possible floatability of a solid in an aqueous environment.

Flotometric investigation of hydrophobic sulphide-diethyl dixanthogen systems

Abstract Different size fractions of hydrophobic galena, pyrite, chalcopyrite, and copper (I) sulphide were floated in a monobubble Hallimond tube at varying diethyl dixanthogen, (EtX) 2 , concentrations. The floatability of the solids was characterized by maximum recovery (recovery after a prolonged, 30 min of flotation) versus particle size curves at a constant (EtX) 2 concentration, and subsequently, by curves relating the mean particle size for which maximum recovery is 50% ( a 50 ) to (EtX) 2 concentration. To compare the floatability of sulphides, the so-called flotometric equation in the form a 50 (ϱ p − ϱ w ) = L was utilized, where ϱ p , ϱ w , and L stand for particle density, density of water and flotometric activity, respectively. This equation accounts for the influence of particle density on flotation. Dixanthogen flotation of several hydrophobic sulphides was evaluated in terms of flotometric activity L versus relative (EtX) 2 concentration expressed as log C / C m , where C m denotes the (EtX) 2 concentration which maximizes the size of particles ( a max ) that can be floated. It was determined that the flotometric activity was identical for all the sulphides investigated, though different (EtX) 2 concentrations were required for comparable flotation results. It wa also established that maximum flotometric activity was similar to that of collectorless flotation of Teflon and oleate flotation of magnetite.

Flotation of germanium n and p with potassium ethyl xanthate

Steady-state potential of the germanium electrode, flotation tests and results of spectrophotometric ATR (Attenuated Total Reflection) measurements of germanium surface in the presence and absence of potassium ethyl xanthate are presented. On the basis of the steady-state potentials of the germanium electrode in ethyl xanthate solutions, the standard potential E0 of the reaction: Ge + 2EtX− = Ge (EtX)2 + 2e is estimated. The pH ranges of the dixanthogen (EtX)2 and the germanium xanthate Ge(EtX)2 species predominance in the bulk solution are calculated. It has been established that flotation of germanium is greater than the natural floatability (in the absence of collectors) in the pH ranges where (EtX)2 or Ge (EtX)2 are present in the bulk solution. Spectrophotometric results reveal the presence of (EtX)2 and Ge (EtX)2 on the surface in the same pH ranges as is calculated for the bulk reactions. No significant differences in the surface properties and the flotation behaviour between germanium n and p have been found.