Jarosite precipitation

Fig. 2. Flow sheet for modified jarosite precipitation process.

The conversion process (developed by Outokumpu) is a modification of the jarosite process and involves simultaneously zinc ferrite dissolution and jarosite precipitation in the same reaction vessel. The overall reaction may be represented in simplified form as ... 

Stahl, R.S. Fawning, D.S. James, B.R. (1993) Goethite and jarosite precipitation from ferrous sulfate solutions. Soil Sci. Soc. Am. J. 

In some circumstances, the oxidation of sulfide minerals to sulfate (oxy)(hydr)oxides involves one or more intermediate steps that are related to the properties of the field location. For example, realgar and orpiment in mining wastes at the Kusa mine in Sarawak, Malaysia, initially weather to arsenolite. The arsenolite readily dissolves in sulfate-rich waters in open pits. As the water evaporates, arsenic-rich jarosite precipitates (Williams, 2001, 274). 

Mineral saturation indices for melanterite and amorphous iron hydroxide agree quite well with field occurrences of the same minerals. Jarosite, however, appears to be supersaturated for nearly all of the samples regardless of the presence or absence of the mineral in these streams. Field observations indicate that jarosite precipitation occurs in the microenvironment of bacterial colonies where the chemical conditions may be quite different from the bulk solution. These considerations lead us to suggest that there is a kinetic barrier which hinders jarosite precipitation but does not hinder ferric hydroxide precipitation and that this barrier is overcome by the surfaces of bacterial colonies (both iron-oxidizers and unidentified nonoxidizers ). ... 

Case 5 Compare with Case 4 to see the effect of jarosite precipitation. pH stabilizes at 5.6. 

With this Hematite process, the step of jarosite precipitation is avoided (v. Rbpenack... 

Since the start-up of the zinc plant, the leaching circuit comprised three main steps neutral leaching, hot acid leaching and jarosite precipitation, as shown in the flowsheet of Figure 1. 

The objective of this step is to extract at least an additional 0.5% of the total zinc going to leaching, "niis is achieved in a high temperature and moderately acidic acid wash of the jarosite residue, to leeich part of the zinc ferrites that are present because calcine is used as the neutralizing agent in the jarosite precipitation step. To install this step, two existing 80 m tanks were refurbished as reactors and a new 500 m thickener was built. 

The increase in the iron content in the zinc concentrate mixture fed to the roaster caused a noticeable decrease in the global zinc recovery of the plant. This occurred mainly because of the higher amounts of residue generated that were not properly washed in the existing filtration equipment. Additionally, the zinc extraction decreased because of the lack of a sufficiently strong attack of the zinc ferrites and the increased use of calcine in the jarosite step that is caused by the increased amount of jarosite precipitated. 

ACID LEACHING OF NICKEL LATERITES WITH JAROSITE PRECIPITATION... 

Keywords Nickel Laterite, Atmospheric Leaching, Jarosite Precipitation, Pressure Acid... 

Jarosite precipitation was further discussed in several papers in the following two decades. Canterford noted in 1975 that [8] ... 

Researchers at the National Technical University of Athens published a number of papers in the 1980s and early 1990s, where jarosite precipitation of iron from nickel laterite acid leach solutions was considered [9, 10, 11, 12]. 

In our previous papers iron removal from sulphate solutions has been studied by precipitation as goethite and by solvent extraction in D2EHPA solutions. In the present paper, jarosite precipitation has been studied. ... 

Whilst BHP Billiton developed a range of technologies in the area of nickel laterite acid leaching, two technologies stand out in the area of atmospheric leaching with jarosite precipitation. These are ... 

Sequential atmospheric leaching of limonite followed by leaching of saprolite with simultaneous jarosite precipitation and acid regeneration, also known as Jarosite Atmospheric Leaching (JAL) [18, 19, 20]. 

Saprolite slurry is then added. Much of the magnesium and nickel is leached, causing the free acid to drop to a level where jarosite precipitation begins, regenerating acid and furthering the leach process. Jarosite Precipitation and acid regeneration are represented by equation 3, with the saprolite leach by equation 4. 

The combined leach slurry passes to induced jarosite precipitation (IJP) and primary neutralization (PN). Recycle streams from downstream processes are leached initially, further decreasing free acid and allowing more jarosite formation to occur. Limestone is then added to decrease iron levels further and neutralize free acid. 

It has been found in practice that the reaction is self-seeding, with sufficient solids available in the agitated tanks to initiate and sustain jarosite precipitation. 

Figure 5. Batch Atmospheric Leach Nickel, Cobalt and Iron Extractions Induced Jarosite Precipitation...

In addition to the hematite precipitation - acid regeneration chemistry, sodium and potassium in seawater react with aluminum in solution to form alunite, resulting in low net extraction. Alunite precipitation also regenerates acid, helping to minimize acid consumption, analogous to jarosite precipitation in atmospheric leaching. Sodium alunite precipitation, as shown in equation 9, is an analogue of jarosite precipitation in equation 3. 

Atmospheric Leach and Precipitation Processes. Aluminum is completely precipitated at the pH used for ferrous iron oxidation. The precipitated aluminum reports to the residue recycle stream and is releached in the Induced Jarosite Precipitation stage. There is therefore the risk of a recirculating load building up in the circuit between the Induced Jarosite Precipitation and Secondary Neutralization circuits. However, the pH of the intervening Primary Neutralization step is sufficiently high to precipitate excess aluminum and provide a safe bleed from the process. 

In the induced jarosite precipitation and primary neutralization processes, this is typically done in-slurry, at temperatures in excess of 80°C. Few issues with scale formation occur, apparently due to the presence of a large surface area available from the leach residue solids, relative to equipment surfaces. It is important to provide adequate retention time for the complete reaction of the limestone, to avoid reactions continuing to occur in downstream thickeners and pipework. Such reactions can lead to both process upsets and scale formation over the longer term. 

Sulfuric acid atmospheric leaching of laterites with jarosite precipitation has proven itself to be a versatile process, capable of treating both limonites and saprolites and variable ratios of these two ore types. 

Of the purely atmospheric leach options presented, sequential limonite - saprolite atmospheric leaching gives the best extractions for a given total acid addition and generally produces a leach slurry ready for further (induced) jarosite precipitation with a minimum of limestone addition. 

P. Maraboutis, A. Kontopoulos,. Jarosite Precipitation from Iron - Nickel - Cobalt Sulfate Solutions , Extractive Metallurgy of Nickel and Cobalt, G.P Tyroler, C.A. Landolt, Eds.,... 

The Ni, Co, Zn, Cu, Mn levels increased during each leach experiment. The Fe levels in solution peak and stay high for most of the first series of four experiments with variable acid addition. For the second series of four higher temperature experiments (with oxygen sparging) there was a marked decrease in the iron in solution with time due to oxidation and precipitation as hydronium jarosite. The jarosite precipitation is a favourable reaction as the acid released upon Fe precipitation continues to leach Ni and other metals. The nickel extraction rose with increased temperature of leaching. 

Acid Teaching of Nickel Eaterites with Jarosite Precipitation.75... 

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