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1

Thermal and acid treatment of diatom frustules

100%

Gulturk E. , Guden M.

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tom Vol. 46, nr 2

196--203

EN

Purpose: Diatoms, belonging to Bacilariophyta family, are single-celled microscopic (1-100 micron) plants living in aquatic environment. The diatom cell is protected inside a shell (frustule) constructed from amorphous nano-silica particles. It is proposed that the frustules and purified silica powders obtained from frustules can be used to reinforce composites. In this study, microstructural properties of two diatom frustules were determined and different methods were investigated for silica powder processing from diatom frustules. Design/methodology/approach: Natural (ND) and calcined (CD) diatom frustules were used in this study. The chemical and microscopic properties of the diatom frustules were determined using Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectrometry (FTIR) and energy dispersive X-Ray Florescence spectrometer (XRF). Two different processing routes were applied to process silica powder from diatom frustules. These included (i) leaching the frustules directly in HF, (ii) incorporating thermally treated frustules in to the liquid nitrogen. Findings: At increasing HF concentrations, the variety of shapes, nanopores and open voids were seen on the surface of frustules as silica particles were removed from the surface. SEM micrograph results showed that HF significantly etched inside the existing pore structure of the diatom frustules. HF concentration was found more effective in mass loss than the leaching time. Thermal treatment induced several cracks propagated between macro pores and nanopores of the frustules. Practical implications: Results show that thermal and acid treatments were not effective for obtaining silica powder from frustules. Ball milling can be used for silica powder processing from frustules in the further study. Originality/value: In this paper, the microstructural properties of ND and CD frustules were determined. The effect of thermal and acid treatment on frustules was investigated with SEM.

2

A comparison of uranium recovery from low-grade ore by bioleaching and acid leaching

75%

Szolucha M. M. , Chmielewski A. G.

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tom Vol. 53, iss. 1

136--149

EN

The objective of this work was to compare the bioleaching with the acid leaching of uranium under similar process conditions within 65 days. The low-grade uranium ore used in the experiments was collected from Radoniow’s ‘small’ dump, Poland. Bioleaching and acid leaching studies were carried out in identical columns. The isolated bacterial consortium from the Radoniow’s mine was used for the bioleaching process. A solution of sulphuric acid and H2O2 as oxidizing agent was used for the acid leaching. The extraction of uranium under acid leaching conditions reached maximum of 64±13 % w/w after 31 days. The bioleaching of uranium achieved a maximum extraction of 75±15 % w/w after 55 days. In this study an attempt was made to demonstrate the relationship between the shrinking-core model and the experimental data by plotting the fractional conversion of uranium against time.

3

Wydzielanie związków żelaza z roztworu po ługowaniu odpadów poflotacyjnych Zn-Pb

63%

Siedlecka E. , Sobik-Szołtysek J.

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tom T. 20, nr 2

263--276

EN

Iron is usually present in the leaching solutions and its elimination is a major problem in hydrometallurgy. The recovery of iron from such solutions is usually carried out by precipitation as jarosite, goethite or hematite. Together with the iron other undesirable metals, mainly Zn, Mg, Pb are precipitated. The impact of the following parameters: temperature, time, type and dose of oxidant on selective separation the iron compounds from the leaching solution of Zn-Pb post-flotation tailings were investigated. The leaching solution was obtained in the process of dynamic neutralization the accumulator electrolyte with the Zn-Pb flotation tailings and separation of the precipitate from the solution. Using the set conditions of iron compounds precipitation from the leaching solution, the post-processed solutions were obtained in which the content of Mg, Zn, Fe were analyzed. It was found that the process of iron compounds precipitation causes co-precipitation of the accompanying metals that contaminate the resulting precipitates. The coprecipitation of magnesium, together with iron compounds is particularly disadvantageous process results in a reduced yield of metal in the final product. In order to minimize these losses, the oxidizing precipitation of iron from the leach solution in the form of goethite was carried out. This led to significant loss of Mg+2 ions from the solution in an amount of 0.24% positively influencing technological process of magnesium sulphate recovery from the waste. The goethite precipitate formed in a simple single stage process is a commercial product or an intermediate product (after ignition) for the preparation of a red pigment.

PL

Żelazo jest często obecne w roztworach po ługowaniu, a jego eliminacja jest głównym problemem w procesach hydrometalurgicznych. Odzysk żelaza z takich roztworów polega najczęściej na jego wydzieleniu w postaci jarosytu, getytu lub hematytu. Wraz z żelazem wytrącają się inne niepożądane metale, głównie Zn, Mg, Pb i inne. W pracy zbadano wpływ takich parametrów, jak temperatura, czas, typ i dawka utleniacza na selektywne wydzielanie związków żelaza z roztworu po ługowaniu odpadów poflotacyjnych Zn-Pb. Roztwór po ługowaniu pozyskano w procesie dynamicznej neutralizacji elektrolitu akumulatorowego odpadem poflotacyjnym i oddzieleniu osadu od roztworu. Stosując ustalone warunki wydzielania związków żelaza z roztworu po ługowaniu, otrzymano roztwory poprocesowe, w których oznaczono zawartość metali: Mg, Zn, Fe. Stwierdzono, iż proces wydzielania związków żelaza, w zależności od warunków, powoduje współstrącanie się towarzyszących metali, które zanieczyszczają powstałe osady. Szczególnie niekorzystnym procesem jest współstrącanie się magnezu wraz ze związkami żelaza powodujące zmniejszenie uzysku metalu w produkcie końcowym. W celu zminimalizowania tych strat przeprowadzono strącanie utleniające żelaza z roztworu po ługowaniu w postaci getytu, uzyskując nieznaczne straty jonów Mg+2 z roztworu w ilości 0,24%, co jest bardzo korzystne dla procesu technologicznego pozyskiwania siarczanu magnezu z odpadów. Wydzielony osad getytu w prostym procesie jednostopniowym stanowi produkt handlowy, a po wyprażeniu - półprodukt do otrzymywania pigmentu czerwonego.