Collector Dosage Research Articles

Study of shear-flocculation of silica

The US Bureau of Mines investigated the fundamental aspects of shear-flocculation using a rapid, in-situ particle size analyzer. Silica was stirred in the presence of an aliphatic amine to determine the effects of collector coverage, stirring speed and solids concentration on the kinetics of shear-flocculation. The results showed that shear-flocculation is a two-stage process. In the first stage, which occurs during the first 1–2 min. of the reaction, the mean particle size increases rapidly, and in the second stage, an equilibrium is set up between the rates of floc growth and floc decay. Collector dosage affected the position of the equilibrium by altering the number of surface sites for particle-particle attachment. A minimum stirring speed was necessary for shear-flocculation, which was dependent on solids concentration and collector dosage. This stirring speed was the minimum necessary for particles to overcome the electrostatic energy barrier, and that results in keeping the conditioned particles dispersed. Larger particles flocculated more rapidly. At very high stirring speeds, large flocs became unstable, resulting in a narrowed particle size distribution in the slurry.

Characterizing Coal Flotation Performance Using Release Analysis

Unlike dense media separation, froth flotation has no widely accepted counterpart to float-sink analysis for characterizing process performance. However, release analysis, developed by C.C. Dell in 1953, could serve as this counterpart by providing a measure of the "state of release" or ultimate separability of a sample by froth flotation. In an attempt to encourage the acceptance of this technique as a standard for characterizing flotation performance, release analysis has been carried out on a variety of U.S. coals including Pittsburgh No. 8, Upper Freeport and Illinois No. 6. Tests conducted as a function of various frother types and frother and collector dosages indicate that the release curve is relatively independent of these parameters. Run-of-mine coals, generally containing large amounts of free mineral matter, produce superior release curves to precleaned samples of the same material, while increased grinding lends to improve the release curve. When compared to centrifugal float-sink analysis, release analysis produces an inferior separation, indicating that float-sink data are not appropriate for characterizing a surface-based process such as froth flotation.

Effect of Collector Dosage on Metal Removal by Precipitation/Flotation

This study examined the effects of various dosages of chemical collectors on the removal in a combined metal hydroxide precipitation and air-flotation of heavy metals from industrial wastewaters. The residual metal concentrations were sensitive to pH, collector dosage, and air-injection rate. The optimum pH for treatment of the industrial wastewaters was 9.18, determined from jar tests. Although this pH does not necessarily represent the maximum removal of any one metal, it represented the optimal removal of the combined metals system. A single collector dosage did not maximize the removal of each metal from the industrial wastewaters used in the study. Metal removals were slightly greater using the nozzle air flotation system as compared to the induced air flotation system. The study also found that a single collector dosage is not effective for all metals, although removals of more than 80% were consistently achieved. The removal of heavy metals and oil appears to occur through a coprecipitation-adsorption mechanism.

A study of the pyrite flotation efficiency of dithiocarbamates using factorial design techniques

The flotation of pyrite using a selection of dithiocarbamate collectors having different alkyl functional groups has been studied. Factorial design techniques were used to determine the importance of the following variables: dithiocarbamate alkyl group type, pH, collector dosage, conditioning time, copper sulphate dosage, and ore particle size or ore condition. The factors which had the greatest effect on the grade and recovery were the alkyl group type, pH and copper sulphate dosage. The highest pyrite yield (83.4% recovery, 19.7% grade) was obtained when using di-n-propyl dithiocarbamate at a pH = 4. In the case of di-n-propyl dithiocarbamate the addition of copper sulphate had little effect on the recovery or final grade whereas in the case of n-propyl and n- and cyclo- hexyl dithiocarbamates addition of copper sulphate had a depressing effect on the flotation of pyrite. Proposals are made to explain these observations in terms of the influence which pH has on the copper ion, dithiocarbamate ion and pyrite surface interactions and the resultant effect on the hydrophobicity of the particle-collector complex.

Moly/copper separation from concentrate of the combined acid and basic circuits at el teniente

Andean mines in Chile process partially weathered copper ores - with about 25% non-sulphide copper - containing significant quantities of molybdenum, silver and gold, whose recoveries are all adversely affected by oxidized minerals, and by the presence of fines, such as limonite, in the pulp. El Teniente ores, however, contain only molybdenum, which has shown a serious drop in recovery (from 48% to 34%), attributed to a greater moly oxide content of the ore, and excessively fine moly particles, as well as the need for too high (12+) a flotation pH in the final cleaner circuits to limit pyrite in the smelter feed. The mine's metallurgical staff is well along in correcting the cause, and the necessary steps have been taken to raise moly recovery back to the 45+% range. These include a reduction in the xanthogen formate collector dosage and changes in the flotation sequence. To arrive at a new processing strategy, it was necessary to measure the effect of changes in pH, grind, and redox potential on the recovery of copper and molybdenum from plant pulp samples. The results of these are reported. Alternate processing schemes studied included a sand/slimes separation and the use of flotation columns in the roughers. cleaners and the moly/copper separation plant. The mining problems encountered in the primary ore zone due to rockbursts has raised the priority of processing the refractory oxide ore, which normally is diluted with clean ore, and which will now have to be processed until primary ore is again available.

An investigation of sub-processes in equilibrium froths (II): the effect of operating conditions

A plug-flow model of a flotation froth was used in a study of the effects of particle size, aeration rate and collector dosage on the behaviour of mineral particles and water in equilibrium froths, i.e., froths from which no concentrate is removed. Testwork was performed on a laboratory scale using three size fractions — 150 to 75 μm, 75 to 38 μm, and smaller than 38 μm — of a pyritic sulphide ore and a phosphate ore. The predictions of the model were in very good agreement with the measured concentration profiles of solids and water with increasing heights in the froth. The transfer factors of the entrained particles decreased with increasing particle size, indicating an increased degree of differential classification between such particles and water as they entered the froth phase from the pulp. The drainage rate constants for the entrained solids decreased significantly with increasing height in the froth, particularly for coarser particles, but those of the water did not change as markedly. The calculated thickness of the bubble films in the froth, as well as the drainage rate constants for the entrained solids, increased with increased aeration rate. The drainage velocities of the solids in the froth decreased slightly with decreasing particle size. There was a marked decrease in the drainage velocities of the coarse particles with increasing height in the froth at low aeration (i.e., in a well-drained froth), which was ascribed to significant interaction between such particles and the walls of the Plateau borders along which they drain. The decreased drainage velocity of the fines was ascribed to an increase in the viscosity of the draining slurry, since wall effects in the Plateau borders were not significant for these particles. Variation of the collector dosage in the range 50 to 200 g t −1 did not significantly influence the parameters of the model.

Fatty acid separation of siliceous carbonate phosphates

The University of Alabama Mineral Resources Institute (MRI) has developed a unique process for selective fatty acid flotation of carbonate gangue from sedimentary apatites (francolite) in the pH range of 4–6 without collector conditioning of the pulp. The process, which does not require an apatite depressant, was modified to beneficiate a high-MgO siliceous phosphate matrix from south Florida. The modified process includes two flotation stages, one for carbonate removal and the other for phosphate recovery from the siliceous gangue. The selective flotation separation of the carbonate and phosphate from siliceous constituents of the matrix at various pH levels and collector dosages are discussed. In the carbonate flotation stage, about 70% of the MgO was rejected in the froth. The phosphate flotation stage produced concentrates analyzing about 31% P2Ov 0.7% MgO, and 4% insol. The overall P2O5 recovery in the two stages was about 85%

The Relationship between the Floatability of Low-Rank Coal and Its Adhesion to Air Bubbles in Aqueous Diacetone Alcohol Solutions

Abstract Aggregative flotation tests of coal rank 31.1 for particle sizes -0.15, -0.25, -0.385, and -0.5 mm at a constant collector dosage (100 kg/t) and at frother reagent dosages varying from 20 to 50 kg/t were carried out. Calculations of the adhesion of aqueous diacetone alcohol (frother reagent) solutions to a coal surface precoated with n-alkanes were also made on the basis of contact angle values asured earlier. The coal flotation results obtained were correlated with the contact angle, work of adhesion, and detachment force of an air bubble from the coal surface. On the basis of the results it was determined that an increase of diacetone alcohol concentration causes an increase of coal recovery and concentrate yield, especially for fine-grained flotation feeds, and the quality of the concentrates decreased simultaneously. It was also found that there is a relationship between the yield of concentrates and the contact angle, the detachment force, and the work of adhesion. The maximal detachment force corresponded to the maximal concentrate yield and the minimal work of adhesion.

An evaluation of the flotation response of coals

The general criteria which must be satisfied by any procedure intended to characterise the fundamental response of a coal to flotation are reviewed. Of the procedures currently advocated, only two, release analysis and the “tree” procedure, satisfy all these criteria. However, the “tree” procedure is demonstrated to be superior in that it more finely discriminates between particles of relatively high but different floatability and that its results are independent of collector dosage. Application of the “tree” procedure to the preliminary design of coal flotation circuits and the measurement of plant flotation efficiency are discussed.

The Simultaneous Removal of Oil and Heavy Metals from Industrial Wastewaters Using Hydroxide or Sulfide Precipitation Coupled with Air Flotation

ABSTRACT A combined chemical-precipitation/air-flotation system was studied to simultaneously remove heavy metals and oil from a synthetic wastewater typically containing 25 mg/L each of copper, lead, and zinc, plus 1000 mg/L of oil. The wastewaters were subjected to hydroxide treatment or sulfide treatment and collectors simultaneously with air flotation. The precipitants were mixed rapidly into solution for 2 min, followed by a flotation time of 4 min. The effects of various collectors and their dosages, as well as the type of precipitant, were examined in terms of removals of oil and heavy metals. Five different chemical collectors were investigated -- sodium lauryl sulfate (NaLS), Atlasep 2A2, Nalco-7182, Nalco-7734, and TFL-365)‡; applied collector dosages ranged from 0 to 1442 mg/L. Removals of heavy metals and oils of at least 93.85% can be attained using this innovative technology. The residual concentrations are sensitive functions of pH, collector type and dosage, precipitant type, and air-injec...

Separation characteristics of different size and density fractions in batch coal flotation

Batch flotation experiments were carried out using two coal samples to study the behaviour of each size and the density fractions in coal flotation. Different size fractions obtained from sizing of concentrates and tailing were subjected to float and sink analysis using organic liquids. The distribution curve technique was adopted to evaluate the performance of flotation. The results show that selectivity of flotation decreases with decrease in particle size. The specific gravity of separation is influenced more by the level of the frother dosage than by the collector dosage. The specific gravity of separation increases with increase in flotation time. The maximum value attained at infinite flotation time increases with decrease in particle size but the rate at which it is reached decreases.

The simultaneous removal of oil and heavy metals from industrial wastewater by joint precipitation and air flotation

AbstractA joint precipitation and air flotation system was used to simultaneously remove oil and heavy metals from an industrial wastewater. The wastewaters were subjected to hydroxide treatment and chemical collectors simultaneously. The flotation tests were run for 4 min. For the particular wastewaters studied, the optimal pH and air injection rate was 9.18 and 12,150 cm3/min, respectively. Three different chemical collectors were investigated (WOF‐67, Nalco‐7182, and Jayfloc‐806*); the optimal collector dosage was typically in the range of 2–5 mg/L (depending on the particular chemical collector and heavy metal of concern). Removals of the heavy metals and oil typically exceeded 85%; oil removals are great as 96.2% were achieved. Removal of the heavy metals and oil probably occurred through a coprecipitation‐adsorption mechanism. Removals of the various heavy metals compared favorably between the individual removal and simultaneous removal (of heavy metals and oil) studies. By appropriate choice of the chemical collector, its dosage, pH and air injection rate, the selectivity for individual metal species can be affected.

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

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.

Surfactant mixtures as collectors in flotation

The adsorption of mixtures from anionic and non-ionic surfactants on scheelite and calcite was tested with different physicochemical methods to determine the amounts adsorbed, the adsorption heats and the electrophoretic mobilities in dependence on surfactant concentration. The results show that in addition to the adsorption of anionic and non-ionic surfactants on the surface of the mineral, the formation of calcium surfactant salts in the mineral suspension should also be taken into account. The precipitation of calcium salts seems to be clearly reduced by the addition of non-ionic surfactants. As proved by flotation tests, the recovery and selectivity are thus increased with reduced collector dosage when the collector mixtures are used.

Beneficiation of Coal Fines by Aggregative Flotation

The effect of various operating parameters on the performance of the aggregative flotation process for beneficiating coal fines was investigated. The recovery of carbonaceous matter was found to be improved by high mixing intensity and by the utilization of preemulsified collector in the aggregate formation stage. The presence of salt in the flotation stage was found to enhance recovery of the aggregates and the use of a three-stage aggregative flotation technique was found to recover more than 95% of the carbonaceous matter while rejecting 94% of the liberated ash (67% of the total mineral matter). This was accomplished using 2 kg of kerosene per tonne of coal while, in contrast, conventional flotation techniques yielded a recovery of 47% at a collector dosage of 7.5 kg/t.

Performance administration: improved responsiveness and effectiveness in public service

The results of flotation, using 2-mercaptobenzothiazole (MBT) and its derivatives, 6-methyl-MBT (MMBT), 6-methyloxy-MBT (MOMBT), 6-propyloxy-MBT (PrOMBT), and 6-pentyloxy-MBT (POMBT) on pure mineral samples showed some important advantages in the flotation of galena at neutral pH and low collector dosages. It has been found that MBT shows a high affinity towards surfaces containing lead and copper but no selectivity. The introduction of a pentyloxy ring substituent led to a change in the adsorption kinetics, as shown by microcalorimetry, and an improvement of the affinity towards galena.The basic mechanism of adsorption of MBT on galena and chalcocite has been studied by thermochemical measurements, showing that the adsorption mechanisms of MBT on both minerals are comparable in the initial step, involving the chemisorption of the collector. At concentrations above monolayer a second surface reaction of MBT on galena has been observed and attributed to an oxidative dimerisation.Comparative experiments on adsorption properties of mercapto-benzo-oxazole (MBO) show the important role of the endocyclic element composition on the sorption process. The endocyclic O-atom in MBO prevents chemisorption on galena whereas strong coordinative bonds will be formed on Cu containing surfaces.

Studies on liquid films

The adsorption of mixtures from anionic and non-ionic surfactants on scheelite and calcite was tested with different physicochemical methods to determine the amounts adsorbed, the adsorption heats and the electrophoretic mobilities in dependence on surfactant concentration. The results show that in addition to the adsorption of anionic and non-ionic surfactants on the surface of the mineral, the formation of calcium surfactant salts in the mineral suspension should also be taken into account. The precipitation of calcium salts seems to be clearly reduced by the addition of non-ionic surfactants. As proved by flotation tests, the recovery and selectivity are thus increased with reduced collector dosage when the collector mixtures are used.