Seawater Flotation Research Articles

Improved understanding of chalcopyrite flotation in seawater using sodium hexametaphosphate

Due to the scarcity of freshwater, the application of seawater has been considered as an alternative in mineral flotation. Previous studies reported that the challenges of using seawater was due to various ions contained, but not many achievements in relieving their negative effects have been obtained. This study systematically investigated the application of sodium hexametaphosphate (SHMP) in chalcopyrite (CuFeS2) flotation in seawater, as well as in the presence of Mg2+ or Ca2+ (two divalent ions displayed the most significantly negative roles on mineral flotation). It was found that the detrimental effects of seawater on CuFeS2 flotation were primarily due to the formed Mg(OH)2 colloids (major) and CaCO3 precipitates (minor) attaching onto CuFeS2, giving rise to a hydrophilic CuFeS2 surface. The presence of SHMP significantly increased CuFeS2 recovery in seawater and in the solution containing Mg2+ and Ca2+. Two beneficial mechanisms due to SHMP were proposed. Firstly, SHMP combined with Ca2+ and Mg2+ to form dissolvable complexes, reducing the formation of hydrophilic Ca and Mg precipitation. Secondly, SHMP reversed the interaction force between CuFeS2 particles and Mg(OH)2 colloids from attractive to repulsive, thereby reducing the attachment of these precipitates onto CuFeS2 surface. This study therefore provides a promising way in utilizing seawater for mineral flotation.

Flotation in Seawater

A classification of flotation processes carried out in concentrated electrolyte solutions, e.g., seawater, is proposed using the most obvious features of these processes: low or high content of Mg2+ and Ca2+ ions, pulp ionic strength, and pH. The first distinguishable group is the processes carried out in NaCl/KCl solutions, about 0.5 M in the case of salt flotation of inherently hydrophobic minerals, and at concentrations about 10 times higher in the flotation of potash ores. In the flotation of sulfide ores, such as nickel or copper ores, with xanthate-like collectors, the xanthate collector is apparently not affected by pulp ionic strength and only adjustment of frother may be required. Content of Mg2+ and Ca2+ ions in seawater is the main difference between such systems and fresh water. The presence of these metallic ions can adversely affect flotation in the pH ranges over which these ions hydrolyse. The successful flotation of Cu-Mo ores typically requires depression of pyrite at high pH values achieved with the use of lime. However, in seawater, flotation of Cu-Mo ores requires removal of the hydrolysis products of the Mg2+ and Ca2+ ions or the use of a pyrite depressant that can be effective over the pH ranges that are much below the pH of hydrolysis. Mg2+ and Ca2+ ions also affect flotation of phosphate ores with fatty acids. In this case, the depression mechanism is not caused by precipitating magnesium hydroxides on the mineral surface but by precipitation of collector insoluble salts, and the same ions are responsible for depression in both cases. In the seawater flotation of Cu-Mo sulfide ores and phosphate ores, the practical solution involves either removal of Mg2+ and Ca2+ ions prior to the flotation or complexation with other reagents.

Use of polyethylene oxide to improve flotation of fine molybdenite

Flotation tests using different size fractions of molybdenite with 50 ppm of Diesel oil and 25 ppm of MIBC, carried out in 0.01 M NaCl solutions and seawater, showed much lower floatability of the −10 μm size fraction. The flotation of this finest size fraction was very much improved with the use of polyethylene oxide (PEO). The tests revealed that the improvement resulted from aggregation of fine molybdenite particles by Diesel oil-PEO emulsion. The flotation in seawater was good only in the pH range from 7 to 9 and it was strongly depressed around pH 10–11. While addition of PEO could improve flotation in the good flotation range over pH 7–9, it was not efficient in the depression range caused by precipitating magnesium hydroxy-complexes/magnesium hydroxide.

Effects of elctrolytes on the stability of wetting films: Implications on seawater flotation

Surface force measurements were conducted using the force apparatus for deformable surfaces (FADS) to better understand the stability of the wetting films formed on hydrophobic surfaces in the presence of KCl and MgCl2. The measurements were conducted using thiol-coated gold surfaces as robust model hydrophobic surfaces. The results obtained in pure water show that the wetting films of water on weakly hydrophobic surfaces are metastable due to the presence of a repulsive double-layer force in the films. At high concentrations of KCl, the wetting films become unstable due to double-layer compression, causing them to rupture. In the presence of MgCl2, both contact angles and hydrophobic forces decrease due to the adsorption of the hydrolysis products such as MgOH+ ions and Mg(OH)2 precipitates on the surface. The FADS data obtained in the present work were analyzed using the Frumkin-Derjaguin isotherm to determine the roles of the short- and long-range hydrophobic forces in determining the stability of the wetting films formed on hydrophobic surfaces. The results of the present study are discussed in view of the roles of electrolytes in seawater flotation.

Biodepression of pyrite using Acidithiobacillus ferrooxidans in seawater

In Cu-Mo deposits it is usual to find considerable amounts of pyrite (FeS2). When processing this kind of ore by flotation, pyrite is rejected using lime to increase the pH to alkaline conditions (pH ∼ 10–12). In the case of using seawater without pre-processing (raw seawater), the lime consumption increases dramatically and the recovery of molybdenite drops due to the precipitation of secondary ions (e.g. magnesium, sulfate, calcium and bicarbonate) on its surface. In order to avoid these negative effects, alternative ways of depressing pyrite should be considered.The current work introduces the use of Acidithiobacillus ferrooxidans, bacteria commonly used in bioleaching, as an alternative to depress pyrite in seawater flotation. This work presents the results of biodepression, at microflotation scale, in three systems: fresh water, saline water (35 g/l of NaCl, which corresponds to the salt concentration in seawater) and seawater. It was determined that when pyrite is bio-conditioned with A. ferrooxidans before flotation, recovery of pyrite at pH 8 drops from 99% to 24% and 34% in fresh water and saline water, respectively. A similar behavior is observed when running the experiments in seawater, where recoveries drop from 97% to 36% in the presence of A. ferrooxidans in flotation at natural pH (7.8–8.2). Results show that it is possible to bio-depress pyrite with A. ferrooxidans in seawater flotation at natural pH.

Effects of water conductivity on microbubble size and distribution for seawater flotation in desalination pretreatment processes

Effects of water conductivity on microbubble size and distribution for seawater flotation in desalination pretreatment processes

The impact of seawater with calcium and magnesium removal for the flotation of copper-molybdenum sulphide ores

The use of seawater in the flotation of copper-molybdenum sulphide ores is becoming increasingly important. However, the complex chemistry by the presence of calcium and magnesium hydroxyl-complexes interferes with the recovery of molybdenite. This study analyzes the impact of pre-treated seawater with calcium and magnesium removal on the floatability of copper-molybdenum sulphide ores. The pretreatment was carried out by a mixture of Na2CO3 and CaO, which promotes the precipitation of calcium and magnesium ions. Three different conditions were compared, (i) flotation in seawater at pH 11.5; (ii) flotation in pretreated seawater with calcium and magnesium removal at pH 11.5; and (iii) flotation in seawater at natural pH, i.e. pH≈7.6. While the copper recovery was similar in all cases, the recovery of molybdenum at high alkaline condition was notably increased when seawater harness was reduced. On the other hand, a high pyrite depression was reached because the oxidizing atmosphere at pH 11.5 allows Fe(OH)3 formation.

An improved flotation test method and pyrite depression by an organic reagent during flotation in seawater

An improved flotation test method and pyrite depression by an organic reagent during flotation in seawater

Effect of Mg2+ and Ca2+ as divalent seawater cations on the floatability of molybdenite and chalcopyrite

Seawater flotation has been applied to mineral processing in areas located far from fresh water resources. However, as seawater has a detrimental effect on molybdenite floatability under alkaline conditions (pH>9.5), its application in the conventional copper and molybdenum (Cu-Mo) flotation circuit is hindered. A fundamental study of the effect of two divalent cations in seawater, Mg2+ and Ca2+, on the floatability of chalcopyrite and molybdenite is presented in this paper. Floatability tests showed that both MgCl2 and CaCl2 solutions depress the floatability of chalcopyrite and molybdenite at pH values higher than 9. Furthermore, Mg2+ exerts a stronger effect than Ca2+ owing to the adsorption of Mg(OH)2 precipitates on the mineral surfaces, as indicated by dynamic force microscopy images. The floatability of chalcopyrite was significantly depressed compared with that of molybdenite in a 10−2MMgCl2 aqueous solution at pH 11. This phenomenon is likely due to the adsorption of hydrophilic complexes on the mineral surface, which reduces the surface hydrophobicity. A reversal of the zeta potential of chalcopyrite in MgCl2 and CaCl2 solutions at pH 11 and 8, respectively, indicated the adsorption of precipitates onto the surface. In contrast, the zeta potential of molybdenite decreased continuously under the same conditions. The floatability test of chalcopyrite and molybdenite in mixed systems showed that selective separation of both minerals should be possible with the addition of emulsified kerosene to a 10−2MMgCl2 solution at pH 11. A mechanism is proposed to explain this phenomenon.

Isolation and Selection of Halophilic Ureolytic Bacteria for Biocementation of Calcium and Magnesium from Seawater

Antofagasta the second region of Chile is known worldwide for its extensive mining activity, mainly in the production of copper, molybdenum, iodine and lithium. It is also one of the driest areas of the world with few sources of fresh water that in addition to the current increase in the development of mining projects, it has generated a strong necessity for sea water uses in industrial processes. Recently some mining companies are evaluating the use of seawater in various processes, including mineral flotation. However, they have determined a low metallurgical recovery mainly of Mo, due to the effect of secondary ions as calcium, magnesium, sulfate and bicarbonate present in sea water, which precipitate at alkaline pH and produce colloids that interfere in flotation.As a biotechnology alternative to increase the recovery of valuable species by flotation in seawater, it has been isolated and characterized selected native halophilic bacteria in the Atacama Desert, which used urea as a source of energy to produce ammonia and CO2. The ammonia increases the pH of carbonate generating means, which provides favorable conditions for the formation and precipitation of Ca and Mg carbonates and secondary ions presented in high concentration in seawater.The results show that from the total isolates, 22% has proven urease activity by the method of Christensen and phenolphthalein. Furthermore, isolates were evaluated for their ability to precipitate these ions by biocementation assay. Those bacterial isolates that precipitate these ions faster were identified phylogenetically and urease activity and microbial kinetics were quantified. Finally the obtained crystals were subjected to electron scanning microscopy and X-ray diffraction determining the morphology of the crystals production and mineralogical composition.

Floatability and Bubble Behavior in Seawater Flotation for the Recovering Copper Mineral

Floatability and Bubble Behavior in Seawater Flotation for the Recovering Copper Mineral

Copper–molybdenum ores flotation in sea water: Floatability and frothability

Laboratory rougher flotation tests were conducted with two samples of Cu–Mo ores in fresh water and in sea water as a function of pH. In both cases Cu recoveries were slightly lower in sea water than in fresh water for a wide range of pH (pH 7–12). Flotation of molybdenite was however strongly depressed in sea water at pH higher than 9.5. Frothers were characterized by measuring froth thickness in a modified laboratory flotation cell as a function of pH, salinity, frother type, and solids content (%). It was found that for all tested frothers, foamability in two-phase systems was better in sea water than in fresh water. However, froth layer thickness measurement showed that frothability also depends on solids content and increases with increasing pulp density. At high solids content (35%) the frothability depended strongly on pH. At pH of 9 it was similar for fresh water and sea water, however, once the pH is raised further frothability increases sharply when the tests are carried out in fresh water, but this was not observed in sea water. The froth in sea water is drier than in fresh water, and this probably also depends on solids content.

Using Flotation to Separate Oil Spill Contaminated Beach Sands

Lab flotation in artificial sea water was used to separate sand-oil mixtures prepared by mixing crude oil with quartz-dominated beach sands. Major factors affecting the separation efficiency for three representative oils (light, waxy, and heavy viscous) were examined through lab flotation tests, vortex experiments, and oil viscosity measurements. Results showed that flotation in sea water can effectively separate the tested sand-oil mixtures which had large contrast in physicochemical properties: (1) aging of sand-oil mixtures reduced the separation efficiency; (2) both the viscosity of crude oil and its adhesion to sand surfaces had major impacts on separation efficiency; (3) addition of small amounts of surfactants could substantially improve the separation efficiency; and (4) for heavy viscous oil, hydrocarbon solvents needed to be added to improve separation because of their solvency and capability in reducing oil viscosity.

Flotation of cobalt-rich ferromanganese crust from the Pacific Ocean

Deposits of ferromanganese crust containing cobalt and nickel occur on the seafloor in the Pacific Ocean near the Hawaiian Islands and Johnston Atoll. This paper describes developmental flotation metallurgy to separate crust from its associated substrate gangue. Important variables in ferromanganese crust flotation include reagent type, aeration rate, conditioning time and agitation intensity, pH, temperature, water type, and feed size distribution. Flotation in seawater of –600–μm (–28 mesh) material assaying 6.2% Mn, 0.2% Co, and 0.13% Ni with diesel fuel-crude tall oil-sulfonate collectors produces concentrates assaying 15% Mn, 0.6% Co, and 0.3% Ni with recoveries of 89 to 94% while removing 62% of the feed weight.