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By Leandro Augusto Viana Teixeira, Angela Avelar, Ruberlan Gomes Silva, Virginia S. T. Ciminelli, Daniel Majuste

Rare earth elements are essential for modern life products and green technologies. Recent supply constraints have boosted the development of rare earth projects after the price peak of 2011. The feasibility of a project depends on the definition of a processing route, which in turn depends primarily on the rare earth mineral, with monazite and bastnaesite representing the two most relevant minerals. Monazite-type ores usually contain high acid consumption impurities, such as iron, aluminum, calcium, magnesium and phosphates, and may also contain prohibitive levels of radioactive thorium in its composition. Based on thermodynamic analysis, the present work discusses the fundamentals of a selective process route for rare earth extraction from monazite ores with high iron content. This process involves sulfation by means of concentrated sulfuric acid and roasting at a high temperature. The route yields high rare earth extraction with low iron and thorium extraction and low acid consumption. Rare earth extractions as high as 80 percent were achieved, while iron and thorium extractions were lower than 1 percent, and acid consumption was lower than 0.34 kg of sulfuric acid per kg of ore. The operational window was compared to the one predicted by thermodynamic modeling, with 700 °C representing the optimal roasting temperature.

By Leandro Augusto Viana Teixeira, Angela Avelar, Ruberlan Gomes Silva, Virginia S. T. Ciminelli, Daniel Majuste

Rare earth elements are essential for modern life products and green technologies. Recent supply constraints have boosted the development of rare earth projects after the price peak of 2011. The feasibility of a project depends on the definition of a processing route, which in turn depends primarily on the rare earth mineral, with monazite and bastnaesite representing the two most relevant minerals. Monazite-type ores usually contain high acid consumption impurities, such as iron, aluminum, calcium, magnesium, and phosphates, and may also contain prohibitive levels of radioactive thorium in its composition. This work presents a thermodynamic analysis of a monazite system and discusses the fundamentals of a selective process route for rare earth extraction from monazite ores with high iron content. This process involves sulfation by means of concentrated sulfuric acid and roasting at a high temperature. The route yields high rare earth extraction with low iron and thorium extractions and low acid consumption. Rare earth extractions as high as 80% were achieved, while iron and thorium extractions were lower than 1%, and acid consumption was lower than 0.34 kg of sulfuric acid per kg of ore. The operational window was compared to the one predicted by thermodynamic modeling, with 700 °C representing the optimal roasting temperature

By VIVEK KASHYAP, PATRICK TAYLOR

Zinc ferrite is the major phase component present in zinc refinery residue (ZRR) and electric arc furnace dust (EAFD). Up to 71 percent zinc ferrite has been reported to be present in ZRR, and in most studies zinc ferrite has been deemed the major phase in EAFD. In 2010, the global annual production of EAFD was 3.7 Mt, with 15.20 kg of EAFD generated per ton of recycled steel [1]. The generations of ZRR and EAFD have been growing over time, requiring a greener approach for the reutilization and extraction of valuable elements. ZRR can be a potential source of zinc, as its zinc content is as high as 30 percent [2,3]. The presence of zinc ferrite makes the extraction of zinc difficult because zinc ferrite is refractory to leaching, and direct leaching is inefficient. The Waelz process is currently employed to extract zinc from EAFD and other metallurgical wastes. The Waelz process operates in the temperature range of 1,100 to 1,500 °C and uses coke as reductant. This study explores a carbon-free and relatively low-temperature process for the selective extraction of zinc from pure zinc ferrite.

By VIVEK KASHYAP, PATRICK TAYLOR

The presence of iron in sphalerite induces the formation of zinc ferrite (ZF) during roasting. Zinc refinery residues (ZRR) and electric arc furnace dust (EAFD) contain a significant amount of zinc ferrite and are difficult to treat. According to the literature, up to 71% ZF has been found to be present in ZRR. The dissolution of zinc ferrite is inefficient even in aqua regia. The Waelz process is an existing process to recover zinc from electric arc furnace dust by reduction using carbon monoxide followed by the volatilization of zinc. In this study, zinc was selectively extracted from zinc ferrite by partial reduction of zinc ferrite at relatively low temperature followed by leaching in dilute sulfuric acid (20 g/L). Pure zinc ferrite samples were partially reduced to zinc oxide and magnetite by using H2 gas as a reductant. The presence of magnetite and zinc oxide was confirmed by X-ray diffraction (XRD) technique. A maximum of 95%zinc extraction was achieved after leaching with sulfuric acid on the reacted samples. The paper also discusses the effect of time, temperature, and concentration of H2 in the reducing gas on the extraction of zinc and iron from ZF.

Sep 16, 2020

By S. Mathur, Pradip

Polyacrylic acid (PAA) was evaluated as a selective flocculant for the dolomite-apatite system. PAA with a molecular weight (MW) of 4 million was found to flocculate both dolomite and apatite. However, the flocculation behaviors of dolomite and apatite were significantly different with 450,000 MW PAA, which was found to be the lowest molecular weight fraction capable of flocculation. In single-mineral tests with a dosage of 2 kg/t PAA, 90% of the dolomite and 35% of the apatite flocculated. Selectivity was achieved in mixed mineral tests. From a feed consisting of an 80:20 mixture of apatite and dolomite, respectively, a concentrate containing 90% apatite was obtained with a 70% recovery. The dolomite rejection was about 75%, which corresponds to a 2% MgO content in the concentrate.

Jan 1, 1997

By S. Mathur

Polyacrylic acid (P AA) was evaluated as a selective flocculant for dolomite-apatite system. P AA of 4 million MW was found to flocculate both dolomite and apatite. However, their flocculation behavior was significantly different with 450,000 MW PAA which was the lowest molecular weight fraction capable of flocculation. In single mineral tests, at a dosage of 2kg/t 90% of dolomite and 35% of apatite flocculated. Selectivity was achieved in mixed mineral tests where apatite of 90% grade at 70% recovery level was obtained in the concentrate from a feed consisting of 80:20 mixture of apatite and dolomite. The dolomite rejection was about 75% which corresponds to 1% MgO in the concentrate.

Jan 1, 1995

By D. W. Frommer

In continuing its long range studies of methods of treating low-grade iron ores, the Bureau of Mines has developed a new selective flocculation, desliming, and flotation procedure that enables effective beneficiation of the finely disseminated ferruginous jaspers of the Marquette range, Mich. The process, developed on a bench scale and later confirmed in the 800-lb/hr pilot plant, comprises dispersion, selective flocculation, desliming to reject fine silica and clay, and flotation of silica from the remainder of minus 400-mesh pulps. Pilot plant flotation of two Marquette range ores, using the selective flocculation procedure on feeds containing 36 percent Fe, yielded iron recoveries of about 84 percent in concentrates containing 65 to 66 percent Fe and 4 to 5 percent silica. These results were metallurgically superior to those obtained when selective flocculation was not used. Also operating characteristics were better, and reagent costs were lower.

Jan 1, 1964

By B. A. Hancock

It is not at all surprising that causticized potato and potato derived amylopectin starch solutions performed much better than their parent starches. Some preparation is required to rupture the starch granules to effect the polymeric adsorption and interparticle bridging necessary for selective flocculation. In laboratory work comparing the deslime performance of causticized and autoclave cooked laboratory corn starch solution preparations, it was found that higher deslime weight rejections, with attendant proportionally greater iron unit losses, occurred with the causticized starch. These results may be specific to the ore involved but they do suggest that cooking and causticizing cause different starch granule rup- ture and/or starch breakdown, which have an effect on desliming response. I calculated from the data in the article that the slimes product grades were high - 24.3% and 20.3% Fe when 53.7% and 54.5% Fe concentrate products were obtained, respectively, in Table 4, and 21% Fe with a 62.6% Fe concentrate in Table 5 - using the natural tailings sample, which had a head of 34.3% Fe. It may be advisable for the authors to consider different starch preparations in future investigations. The combination of upgrading and selectivity results presented in Table 4 are not as good as the authors suggest. The authors' claim that a system has been developed to produce saleable concentrates from the Kudremukh tailings is quite disconcerting. There are many hurdles yet to be crossed before commercial application of selective flocculation becomes possible because differ- ences between the very small-scale laboratory tests conducted and commercial application are rather large. Among the many differences are varying circuit feed grades that will occur from use of tailings, the apparent face that much lower tailings grades will be encountered in practice (it is much easier to achieve a high concentrate grade with reasonable recoveries using 34.3% Fe tailings as in the study rather than 25.3% Fe tailings grades that the plant apparently averages), the hydraulic nature of the thickeners used in operations compared to the static system used in laboratory tests, the different size distributions that will be obtained from a plant closed grinding- classification circuit, and differences in water used in a plant operation and the laboratory. The authors wrote that it was necessary to overgrind to be sure that the coarse gangue would not settle with the iron oxide floccules. This situation is likely to be exaggerated in commercial operations where it is assumed cyclones would be used for classification. Because cyclone classification is greatly influenced by particle densities, there will probably be an even greater difference in size between the iron and gangue particles in the plant, which would make the gangue slightly coarser still in relation to the iron. This would make the selective flocculation-desliming separations using the procedure employed by the authors even more difficult and, using the dispersant system the authors employed, greater overgrinding would be required. To grind finer to minimize the coarse gangue in the flocculated iron oxides is quite inefficient and appears not to broach the problem. The actual problem appears to be insufficient dispersion of the ground pulp. In this situation, addition of a dispersant would likely be required to attain a sufficiently high pulp dispersion level to efficiently effect a selective flocculation-desliming separation. Although the very coarse particles would still have a tendency to settle with the floccules, it probably would be found unnecessary to overgrind as much as indicated. Use of an optimum combination of dispersant and pH modifying reagents may also significantly improve the selectivity of desliming. Additionally, although it is possible that sufficient dispersion may be obtained by pH control alone in some situations, it is quite probable that added dispersity was obtained in the reported work from using distilled water. It is research experience that distilled water enhances dispersion. In commercial operations it may not be expected that sufficient dispersion will be obtained by pH control alone, unless the water used in the process is by nature quite dispersive. Overall, a change in the Kudremukh tailings dispersant scheme appears necessary where a dispersant is used in conjunction with a pH modifying reagent. With this change, different dispersion-flocculation responses will result that would have to be further evaluated. Therefore, it is still an open question whether an efficient and effective selective floccula- tion separation using Kudremukh tailings may be obtained that will produce saleable concentrates.

Jan 1, 1987

By T. A. P. Sankar, S. Gundiah, Pradip, R. A. Kulkarni

Two modified polyacrylamide flocculants, namely polyacrylamide with glycolic acid functionality (PAMG), and a copolymer of acrylamide with N-acryloyl-[T]- aminobutyric acid (HPVP), were synthesized, characterised and evaluated for selective separation in apatite/quartz and apatite/dolomite/calcite systems, respectively. PAMG flocculant was found selective in the separation of tricalcium phosphate (TCP) from its mixtures with quartz at acidic to neutral pH range. The selectivity deteriorated at alkaline pH. In contrast, polyacrylic acid (PAA) flocculant was found most effective only in the alkaline pH range. HPVP flocculant (even though flocculating all three minerals namely apatite, dolomite and calcite) was observed to be quite selective for the separation of calcite from apatite-dolomite minerals in single mineral tests in the presence of sodium hexametaphosphate dispersant at neutral pH. There was, however, no selectivity observed during tests on synthetic mixtures. This loss in selectivity is attributed to the phenomenon of hetero-flocculation, as reported earlier, for separation in an apatite-dolomite system with polyethylene oxide.

Jan 1, 1993

By Y. H. Zhan

In beneficiation of phosphate ores it is common to use screening to produce the coarse "pebble" concentrate, and flotation to process the -1+0.1 mm size fraction. The -0.1 mm desliming product is treated as tailings. A new partially hydrophobic flocculant, P(MAAA) latex was developed to enhance flotation recovery of fine apatite particles through selective flocculation.

Jan 1, 2002

By Y. H. Zhan

A new P(MAAA) latex was developed and used in separation of ultrafine apatite from calcite and silica by means of selective flocculation. The latex was found to flocculate selectively apatite from apatite/calcite and apatite/silica mixtures in the presence of sodium tripolyphosphate and sodium silicate over a pH range from 9.1 to 9.4. The separation of apatite from calcite was more selective with sodium tripolyphosphate, while the results of the separation of apatite from silica were better when sodium silicate was used. In the apatite/calcite system, 90% apatite recoveries into a concentrate containing 34% P2O5 were possible in the presence of 4 mg/l of sodium tripolyphosphate at a latex dosage of 2.2 kg/t. In the apatite/silica system, 80% of apatite could be recovered into a concentrate containing 33% P2O5 in the presence of 20 mg/l of sodium silicate at a latex dosage of 1.1 kg/t. Deposition tests were used to study the interaction between the latex and the mineral surfaces. The results revealed that deposition density of the latex on apatite was higher than on calcite; the differences between the deposition onto these two minerals were higher at pH 9.2 than at 7.2. The results point to the stronger interaction between the latex and apatite surface when compared with the latex-calcite interactions.

Jan 1, 1998

By R. W. Smith, J. Dubel, M. Misra

The bacterium Mycobacterium phlei is highly hydrophobic and negatively charged. It has specificity for selective adhesion to fine coal particles, mainly due to hydrophobic interaction. However, it does not attach to pyrite and ash forming minerals present in the coal matrix. Results have shown that this bacterium is an excellent flocculant for fine coal. Not only, are the coal particles visibly aggregated, but the optical micrograph has shown that the coal particles are held in the aggregate by adhesion and bacterial bridging. With Mycobacterium phlei, the flocculation characteristic of coal is markedly different from that usually observed with synthetic polymeric flocculants. In particular, the entwining characteristics of the long chain molecules of synthetic flocculants are absent in the case of Mycobacterium phlei. Since the hydrophobic interactions between the adhering particles are of greater importance in the formation of particle aggregation, the flocculation process is very selective.

Jan 1, 1994

By M. Misra

Jan 1, 1992

By H. Sis, D. Dahlin, S. Chander, C. Summers

Bench-scale selective-flocculation tests were conducted on samples of Florida phosphate and Western phosphate process tailings to recover upgraded phosphate concentrates. After physical and mineralogical characterization, the slurry samples were treated with a broad suite of flocculants with a range of molecular weights and anionic functional groups. Parameters investigated included pH, dispersant and flocculant types, and dose; conditioning parameters and settling times were, for the most part, held constant. Where selectivity was achieved, phosphate minerals remained dispersed, whereas silicate minerals flocculated and settled. Single-stage tests using reagents with low to medium anionic characteristics produced upgraded phosphate concentrates at moderately elevated pH. Two- stage site-blocking tests, in which low-molecular-weight flocculants were used as site-blocking agents, gave improved results.

Jan 1, 2002

By H. Sis, D. Dahlin, S. Chander, C. Summers

Bench-scale selective-flocculation tests were conducted on samples of Florida and Western phosphate process tailings. Physical, mineralogical, and surface characteristics were determined for both types of samples. The flocculation tests investigated dispersant and flocculant types and doses, pH, and slurry percent solids, while other parameters were held constant. Where selectivity was achieved, phosphate minerals remained dispersed, whereas silicate minerals flocculated and settled. In single-stage tests, flocculants having low to medium anionic character effectively upgraded products at moderately elevated pH. Multiple-stage tests, and tests in which flocculants of lower molecular weight were used as site-blockers, gave improved results.

Jan 1, 2002

By Pradip

It is possible to beneficiate low-grade phosphate ore slimes containing predominantly siliceous gangue by a combined selective flocculation-flotation scheme using commercially available reagents. The presence of clays, in particular, montmorillonite and attapulgite, has a disastrous effect on the efficiency of separation. Suitable remedies to overcome this problem are not yet available. Intensive R&D efforts are required in the areas of the design and synthesis of specific reagents, the effect of particle size, and the design of appropriate process equipment to carry out flocculation and flotation of slimes.

Jan 1, 1989

By K. Gum, W. C. Hirt, D. A. Rice

Selective flocculation was used to produce a superclean zinc concentrate by minimizing silica contamination. Research was carried out on a flotation concentrate from the Jersey Miniere Zinc Company (JMZ) in Gordonsville, TN. The material was first dispersed with sodium silicate and then causticized tapioca starch was used to selectively flocculate the sphalerite, leaving the silica in suspension. This technique has been applied commercially to iron ore beneficiation but never to zinc processing. The feed material assayed 0.45% SiO2. The use of 0.56 kg/ t (1.13 lb/st) sodium silicate and 0.070 kg/t (0.141 lb/st) causticized tapioca starch resulted in a 98.2% zinc recovery and produced a purified zinc concentrate assaying 66.0% Zn and 0.24% silica. The target level for silica contamination in JMZ zinc concentrates is currently 0.30% Si02. This work demonstrated that selective flocculation is a potential method for cleaning flotation concentrates, particularly where low silica products are required.

Jan 1, 1995

By W. C. Hirt

Selective flocculation was used to produce superclean zinc concentrate with minimized silica contamination. Research was carried out on a flotation concentrate from the Jersey Miniere Zinc Company (JMZ) in Gordonsville, Tennessee. The material was first dispersed with sodium silicate and then causticized tapioca starch was used to selectively flocculate the sphalerite, leaving the silica in suspension. This technique has been applied commercially to iron ore beneficiation but has never been used for processing zinc. The feed material assayed 0.45% Si02. Use of 0.56 kg/tonne (1.13 lb/st) of sodium silicate and 0.070 kg/tonne (0.141 lb/st) of causticized tapioca starch resulted in 98.2% zinc recovery in a purified zinc concentrate assaying 66.0% Zn and 0.24% silica. The present target level for silica contamination in JMZ zinc concentrates is 0.3% Si02. This work has shown that selective flocculation offers a potential method for cleaning flotation concentrates, particularly where low silica products are required.

Jan 1, 1993

By Yosry A. Attia

One of the most significant advances in Mineral Processing in recent years, is the development of the selective flocculation technology. The technology is primarily aimed at recovering the mineral values from ultrafine ore suspensions. This is achieved by selectively aggregating the mineral particles in question to such size as to enable their effective separation from the suspension. Selective flocculation utilizes the differences in the physical-chemical properties of the various mineral components in the mixed suspension. It is based on the preferential ad- sorption of an organic flocculant on the particular solids to be flocculated, leaving the remainder of the particles in suspension. In order to understand the mechanics of this process, selective flocculation may be divided into four major sub processes; these being: ore slurry dispersion, in which all the particles are stably and uniformly distributed in the suspension with the individual particles being essentially separate; flocculant selective adsorption and floc formation; floc conditioning, which aims at obtaining flocs with desire properties for their subsequent separation and with minimum entrapment of dispersed particles; and floc separation from the suspension. These sub processes will be reviewed later in this article.

Jan 1, 1982

By M. A. D. Azevedo, J. D. Miller, R. Kobler, E. Mutkowska

Up to 3 million tons of automotive shredder residue (ASR) is generated annually in United States. Plastics are the most valuable component of the ASR material making up approximately 25% of the total weight. In order to reuse these plastics, a selective process is required to separate each plastic, with very high purity and favorable economics. One separation technique, which may be able to selectively recover the plastics from ASR, is flotation. The preliminary flotation results have demonstrated that acrylonitrile-butadiene-styrene (ABS) and polycarbonate (PC) can be selectively separated from the model ASR feed, the PC/ABS/PA 66 system, by appropriate control of the surface chemistry.

Jan 1, 2001