@conference{
author = "Đokić, Jovana and Gajić, Nataša and Anđić, Dimitrije and Kamberović, Željko",
year = "2023",
abstract = "During the conventional roast–leach–electrolysis (RLE) zinc production process,
precipitation of the jarosite-type compounds is widely used to remove iron and other metal
impurities from the solution. Above mentioned compounds, with the general formula
MFe3(SO4)2(OH)6, (M+=NH4, Na, K, Ag, etc.), in addition to iron, contain a high
concentration of Pb, Cd, Cr, As, Zn, In, Ga, Ge as metal oxides and/or sulfates [1].
Consequently, jarosite is considered hazardous yet valuable waste [2]. In addition, every
year around 6-7 million tonnes of jarosite waste is generated globally [3]. Due to large waste
volumes and its chemical characteristics, jarosite requires a lot of storage space and
monitoring. Unfortunately, this type of waste is often landfilled causing serious
environmental problems and irreversible metal and value losses. Hence, an urgent solution
for both managing and utilization/recycling is required, to face needs regarding ecological
demands and circular economy goals.
In this paper, jarosite sludge, as a specific type of hazardous industrial waste, is used
to investigate transformation to the targeted compounds through the comprehensive
thermodynamic analysis and experimental roasting process tests. The roasting was
conducted to transform iron into insoluble hematite (Fe2O3), valuable metals (Zn, Cu, and
In) into water-soluble sulfates, and to keep Pb in the form of water-insoluble anglesite
(PbSO4). The solid residue obtained after roasting was used in leaching tests to further
evaluate the efficiency of the targeted phase transformations.
Theoretical considerations of chemical reactions and phase thermodynamics were
performed using the HSC Chemistry v.9.2.3 software [4] to define potential chemical
reactions, examine the feasibility of the target transformations, and set the limiting reaction
parameters. Further, in the first part of the experimental work, the influence of the roasting
process and reaction parameters on the transformation of jarosite sludge phases into target
compounds was investigated. This included variations in the reaction time, temperature, and
furnace atmosphere influence. The leaching conditions were kept constant (temperature of
25 °C, during 60 min, and solid to liquid ratio of 1/5) to determine the efficiency of phase
transformations in the samples obtained by roasting. Changes in the chemical and
mineralogical composition and microstructure were analyzed using different analytical
methods, including XRD and SEM analysis.
According to the obtained results of the roasting process, it was determined that the
phase transformation of jarosite sludge compounds into targeted insoluble hematite and
water-soluble sulfates occurs at 730 °C, the time required is 60 min in the air (oxidizing) atmosphere of 1-2 [dm3/h]/kg of the input material, which is in accordance with the results
of the theoretical indications. Also, it is experimentally confirmed that the introduction of
sulfate into the roasting atmosphere leads to the incomplete transformation of jarosite and
the formation of the unwanted Fe2(SO4)3. Leaching results of the sample obtained by the
abovementioned optimal roasting conditions show that only 4.5 % of Fe is leached while
the rest remains as solid targeted hematite. Also, more than 75 % of In and more
than 90 % of other targeted metals (Cu and Zn) are leached, indicating the high efficiency
of the roasting process. Phase transformation was confirmed by SEM analysis, showing that
hexagonal crystals of jarosite, dominating in the starting material, were completely replaced
with the globular microstructure of Fe2O3, in the roasted samples. SEM analysis of the
leaching residue also confirmed the absence of the water-soluble sulfates and the presence
of the anglesite as water-insoluble sulfate. The phase composition of the samples is
confirmed by XRD analysis.
This research shows that the proposed process enables the recycling of jarosite through
metal transformation and further utilization. The obtained products can be used in industry,
while the metal ions can be selectively separated from the sulfate solution and returned to the
production streams. This approach contributes to the utilization of jarosite, as hazardous
waste, in order to obtain valuable metals, and generally reduces the negative environmental
impact by decreasing the amount of disposed waste and reducing the need for primary
exploitation.",
publisher = "Beograd : Srpsko hemijsko društvo",
journal = "9. simpozijum Hemija i zaštita životne sredine EnviroChem2023",
title = "Jarosite sludge - utilization and valuable metals recovery applying roasting-leaching process",
pages = "180-179"
}
