Hydrometallurgical extraction and reclamation pdf
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- Hydrometallurgical extraction and reclamation
- Hydrometallurgical Extraction and Reclamation
- Copper extraction
The state of the art for the recovery of metals from steel industry by-products using hydrometallurgical processes is reviewed. The steel by-products are different slags, dusts, and sludges from a blast furnace BF , basic oxygen furnace BOF , electric arc furnace EAF , and sinter plant, as well as oily mill scale and pickling sludge.
The review highlights that dusts and sludges are harder to valorize than slags, while the internal recycling of dusts and sludges in steelmaking is inhibited by their high zinc content.
Because wide variations in the mineralogical composition and zinc content occur, it is impossible to develop a one-size-fits-all flow sheet with a fixed set of process conditions. The reason for the interest in EAF dust is its high zinc content, by far the highest of all steel by-products. However, EAF dust is usually studied from the perspective of the zinc industry. In many chemical processes, only the ZnO dissolves, while the ZnFe 2 O 4 is too refractory and reports to the residue.
It only dissolves in concentrated acids, or if the dust is pre-treated, e. The dissolution of ZnFe 2 O 4 in acidic solutions also brings significant amounts of iron in solution. Finally, due to its high potassium chloride content, sinter-plant dust could be a source of potassium for the fertilizer industry.
Producing one ton of steel in an integrated steel plant generates about half a ton of by-products, i. Minor by-products include sinter-plant dust, oily mill scale, and pickling sludge. Although most steel slags have applications, dusts and sludges are often seen as waste. Research is turning to the valorization of those steel by-products that have no applications yet.
The motivation can be the valorization of the metal content. However, in most cases the removal of metals inhibits the recycling of by-products. For instance, the zinc content of BF and BOF sludges is too low for zinc recovery, but too high to recycle the by-products to the BF via the sinter plant. Stewart and Barron suggested the reason for the sensitivity to zinc is that, once charged into a blast furnace, any zinc component is reduced to elemental zinc [ 1 ].
These deposits affect the solid and gas flows through the furnace, so damaging the lining through burden slips. Zinc is also known to attack refractories in the upper stack of the furnace, thus shortening its operating life. Therefore, landfilling or internal stockpiling is often the only option. Most studies were performed on dusts and sludges with only a few references to slags , primarily on EAF dust, because it is sufficiently Zn-rich to be a secondary resource, making extraction economically attractive.
With respect to pyrometallurgical processes, hydrometallurgical routes have several advantages. First, the capital expenditure CAPEX required is lower, making them more suitable for small-scale operations.
As a result, the by-products do not require transport over long distances to large processing plants, such as Waelz kilns. Second, the operating expenses OPEX can be lower, because less energy is used. Third, hydrometallurgical processes are often more selective, so they can be more efficient.
This paper reviews the state of the art for the recovery of metals from steel-industry by-products using hydrometallurgical processes. The steel by-products are different types of slags, dusts, and sludges from a blast furnace BF , basic oxygen furnace BOF , electric acid furnace EAF , and sinter plant, as well as the oily mill scale and pickling sludge.
The literature covers the period to March , and this review complements others on the valorization of steel-industry by-products [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ].
The slag is crushed and screened air-cooled slags or granulated. The remainder is reused internally by steel plants for roadmaking and landfills. There are currently no technical limitations on the use of BF slags. Granulation is becoming the standard route, with cement being the high-value application. In other words, BF slag has been promoted from a by-product to a co-product. Because there are no toxic or valuable metals, there is no need to hydrometallurgically treat BF slag to remove and recover metals.
An exception are the slags produced from Ti-rich iron ores. These also contain vanadium and chromium, which are reduced by the coke in the BF and report to the hot metal. In contrast, vanadium and chromium are oxidized in a BOF, where they are enriched in the BOF slag, usually called vanadium slag [ 12 ]. The grade of Ti-bearing slags is too low to recover the titanium and produce TiCl 4 or TiO 2 , but too rich for use in the cement industry.
As such, hydrometallurgical routes recover the titanium from these slags with concentrated H 2 SO 4 [ 13 ]. But with mild conditions, less co-dissolution occurs. Much more titanium was recovered from water-quenched and naturally cooled slag. Valighazvini et al. He et al. It is also possible to dissolve part of the matrix, which results in a residue with enough TiO 2 for use as a secondary raw material.
Mang et al. The REEs were stripped from the loaded organic phase by oxalic acid. However, this is uneconomic at present, because of the low concentration of REEs, e. BF slag can be used for CO 2 sequestration with the leaching-carbonation process [ 18 , 19 , 20 ]. Here, the calcium in the slags is solubilized, using acetic acid or ammonium salts, and the dissolved calcium is precipitated as pure CaCO 3 by carbonation.
Compared to BF slag, converter slag is difficult to recover. Both can hinder applications through expansion, a high fines content and a high pH in water. The high free-lime content is a problem in applications like aggregates, but can be used for fertilizers and cement. BOF slags can be internally recycled to the sinter plant, the BF or the converter. External applications include fertilizers, soil conditioners, cement components, raw material for clinker or rock wool, filler for concrete, and absorbent for wastewater pollutants.
As with BF slag, converter slag is used for CO 2 sequestration, with the high lime content being an advantage. Phosphorus reports to the hot metal and comes back in a loop to the converter, where it must be removed by consuming more lime and generating more slag, which is a costly process.
In general, the heavy-metal content of converter slags is not problematic, but there is concern about the chromium content of slags used for clinker production. The chromium in slag is trivalent, but it can be oxidized in the clinker kiln and become the hazardous hexavalent chromium. BOF secondary-metallurgy SM slag has a chemical composition different to that of converter slag and so these slags should be kept separate.
However, a high Al 2 O 3 content is undesirable for recycling in a sinter plant. This type of slag is used in construction, particularly for roads; however, about one-third is landfilled. The main problem with desulfurization slag is the high content of sulfur, alkali, free lime, and sometimes fluorine.
This makes it more difficult to valorize than converter slag. It also contains metal droplets, so that metal recovery is required.
Some of these slags are recycled via the sinter plant or the EAF and some to road construction. Vanadium co-occurs with iron, titanium, manganese, aluminum, and silicon. The main mineral phases in vanadium slag are fayalite Fe 2 SiO 4 , titanomagnetite Fe 2. Chromium spinel phases can also be present. Vanadium slag is an important resource of vanadium. The molten NaOH roasting method can extract vanadium from vanadium slag. But this process uses a lot of energy and NaOH, making it costly.
The conventional approach to recovering vanadium is roasting with NaCl, followed by water leaching, purification of the vanadium solution, and precipitation of the vanadium as ammonium polyvanadate NH 4 V 3 O 8. Finally, calcination yields vanadium pentoxide V 2 O 5. The purpose of roasting with NaCl or other sodium salts is to convert the spinel phase into soluble sodium vanadate NaVO 3. Chromium spinel, which is commonly found in vanadium slag, can be partially oxidized to hexavalent chromium when roasting with sodium salts [ 23 ].
This generates a lot of chromium sludge, and so new vanadium-extraction technologies have been developed. Adapted from [ 22 ]. By roasting with CaO, the problem of sodium salts can be avoided [ 23 , 24 ]. The leaching involves dilute H 2 SO 4 [ 23 ]. However, there are operational difficulties and a low vanadium recovery.
Furthermore, during acid leaching, calcium sulfate accumulates in the residues, inhibiting further use as a raw material. Leaching is easier with ammonium carbonate, since it allows the selective leaching of the vanadium into the liquor from calcification-roasted vanadium slag, but maintains the phosphorus in the solid phase because of the differences in the reactivity of calcium vanadate and calcium phosphate with ammonium carbonate [ 25 ].
Vanadium was recovered from Ca-rich slags by direct oxidative roasting, without added salt, followed by leaching with a sodium carbonate solution [ 26 ]. To recover the vanadium and titanium, the vanadium slag was roasted with ammonium sulfate at moderately high temperatures, followed by dilute H 2 SO 4 leaching [ 27 ]. To enhance the extraction, an activation pre-treatment of the vanadium slag via high-temperature water quenching was employed.
Li et al. This can be recycled in the process and the leaching residue can be returned to the blast furnace Fig. The vanadium is recovered as ammonium vanadate NH 4 VO 3. Instead of ammonium carbonate, ammonium oxalate was found to be an efficient lixiviant [ 29 ]. Adapted from [ 23 ]. Flow sheet for vanadium extraction from vanadium slag via non-salt roasting and ammonium salt leaching. Direct vanadium leaching with acids, without prior roasting, is efficient and has no emission problems.
Unfortunately, it consumes a lot of acid and has poor selectivity. Zhang et al. To mitigate the acid consumption, waste acids have been proposed [ 31 ]. To mitigate the low selectivity, the leachate can be purified by solvent extraction. For instance, Zhang et al.
Hydrometallurgical extraction and reclamation
Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper consists of a series of physical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations , and other factors. As in all mining operations, the ore must usually be beneficiated concentrated. The processing techniques depend on the nature of the ore. If the ore is primarily sulfide copper minerals such as chalcopyrite , the ore is crushed and ground to liberate the valuable minerals from the waste 'gangue' minerals. It is then concentrated using mineral flotation.
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Hydrometallurgical Extraction and Reclamation. By E. Jackson, Ellis Horwood Limited, Halsted Press, Chichester, , pp., $4 · Related · Information.
Hydrometallurgical Extraction and Reclamation
NCBI Bookshelf. This chapter outlines the basic steps involved in mining, processing, and reclamation that might be suitable for uranium ore deposits in the Commonwealth of Virginia. For uranium ore deposits, the choice of mining methods and processing options is very deposit-specific and dependent on many variables such as the quality and quantity of the ore, the shape and depth of the ore deposit, site-specific environmental conditions, and a range of other factors.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. However, uranium mining and processing add another dimension of risk because of the potential for exposure to elevated concentrations of radionuclides.
Hydrometallurgy is a technique within the field of extractive metallurgy , the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Hydrometallurgy is typically divided into three general areas:. Leaching involves the use of aqueous solutions to extract metal from metal bearing materials which is brought into contact with a material containing a valuable metal.
The state of the art for the recovery of metals from steel industry by-products using hydrometallurgical processes is reviewed. The steel by-products are different slags, dusts, and sludges from a blast furnace BF , basic oxygen furnace BOF , electric arc furnace EAF , and sinter plant, as well as oily mill scale and pickling sludge. The review highlights that dusts and sludges are harder to valorize than slags, while the internal recycling of dusts and sludges in steelmaking is inhibited by their high zinc content. Because wide variations in the mineralogical composition and zinc content occur, it is impossible to develop a one-size-fits-all flow sheet with a fixed set of process conditions. The reason for the interest in EAF dust is its high zinc content, by far the highest of all steel by-products. However, EAF dust is usually studied from the perspective of the zinc industry. In many chemical processes, only the ZnO dissolves, while the ZnFe 2 O 4 is too refractory and reports to the residue.
Hydrometallurgical Extraction and Reclamation. By E. Jackson, Ellis Horwood Limited, Halsted Press, Chichester, , pp., $4 F. M. Doyle. University.
Hydrometallurgical extraction and reclamation
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