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1

Effect of particle size on chalcocite dissolution kinetics in column leaching under controlled Eh and its implications

Phyo Htet Aung, Jia Yan, Tan Qiaoyi, Zhao Shenggui, Liang Xinxing, Ruan Renman, Niu Xiaopeng

Physicochemical Problems of Mineral Processing

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2020

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Vol. 56, iss. 4

676--692

EN

Natural high grade chalcocite samples were leached in column under controlled Eh, constant temperature and solution pH to investigate the effect of particle size on dissolution kinetics. Moreover, low grade ores of larger size fractions were leached in column using raffinate from the industrial heap as an irrigation solution to simulate the real heap conditions. The leaching rate of large particle sizes (31-200 mm) were very slow without inflection point which are normally present in the leaching of small particle sizes (0.054-31 mm). The effect of particle size was more remarkable in the dissolution of large particles than that of small particles during the first stage (<45% dissolution). However, the dissolution rate of the second stages (>45% dissolution) were not noticeably affected by the particle size. Results of kinetics analysis of leaching of small particles using shrinking core model indicated that the first stage was controlled by fluid diffusion and confirmed by the low activation energies (20.98 kJ/mol). The kinetics of second stage was controlled by chemical reaction and product layer diffusion and the later control became prominent with increasing particle size. Similarly, product layer diffusion was the rate-controlling step for the first and second stages of leaching of large particles. X-ray CT and SEMEDS studies observed the increasing numbers of cracks and porosity and the formation of sulfur layer on the surface of the residue samples. The findings in this study provided some useful implications to optimize the heap performance and understand the leaching behavior of large particles.

2

Study of the reaction between dolomite and nitric acid

Pultar Martin, Vidensky Jan, Sedlarova Ivona

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

370--379

EN

This paper is focused on the kinetics of the reaction between natural dolomite and diluted solutions of nitric acid at various temperatures. All experiments were carried out in a semi-batch reactor with an approximately constant nitric acid concentration using the pH-stat titration method. The reaction was studied in the temperature range from 293 to 353 K and the nitric acid concentration in the range from 0.001 to 0.200 mol dm-3. The strong effects of both temperature and nitric acid concentration were observed. The determined fractional values of the apparent reaction order (0.39 to 0.75) indicate a very complex reaction mechanism. In the studied concentration range, the values of the apparent activation energy increase from 30 to 58 kJ mol-1. Based on these data it can be assumed that the reaction takes place in the transitional regime with the stronger influence of chemical reaction. This assumption was verified by calculation of the nitric acid concentration on the surface of the dolomite grain using Sherwood criterion equation. The change in the role of the rate-controlling step was found for highly diluted solutions (< 0.010 mol dm-3 HNO3).

3

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

Szolucha M. M., Chmielewski A. G.

Physicochemical Problems of Mineral Processing

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2017

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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.

4

Microbial Leaching of Chromium From Solidified Waste Forms – a Kinetic Study

Ayyappan C. S.

Journal of Ecological Engineering

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2015

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Vol. 16, nr 3

36--42

EN

In this study, Thiobacillus thiooxidans (T. thiooxidans) was used to study the microbial stability / degradation of cement-based waste forms. The waste forms contained a chromium salt (CrCl3·6H2O), cement and other additives viz., lime and gypsum in two different proportions. The experimental samples of all the simulated waste forms showed evidence of microbial growth as indicated by substantial increase in sulfate. Chromium leached from the waste forms was found to be lowest in cement – lime solidified waste forms (0.061 mg·1-1) and highest in cement gypsum waste forms (0.22 mg·1-1) after 30 days of exposure. These values were lower than the toxicity characteristic leaching procedure (TCLP), regulatory limit (5 mg·1-1). Model equations based on two shrinking core models (acid dissolution and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement based waste forms. The bulk diffusion model was observed to fit the data better than the acid dissolution model, as indicated by good correlation coefficients.

5

Adsorption of Zn(II) ions from aqueous environment by surface modified Strychnos potatorum seeds, a low cost adsorbent

Senthil Kumar P.

Polish Journal of Chemical Technology

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2013

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Vol. 15, nr 3

35-41

EN

The surface modified Strychnos potatorum seeds (SMSP), an agricultural waste has been developed into an effective adsorbent for the removal of Zn(II) ions from aqueous environment. The Freundlich model provided a better fit with the experimental data than the Langmuir model as revealed by a high coefficient of determination values and low error values. The kinetics data fitted well into the pseudo-second order model with the coefficient of determination values greater than 0.99. The influence of particle diffusion and film diffusion in the adsorption process was tested by fitting the experimental data with intraparticle diffusion, Boyd kinetic and Shrinking core models. Desorption experiments were conducted to explore the feasibility of regenerating the spent adsorbent and the adsorbed Zn(II) ions from spent SMSP was desorbed using 0.3 M HCl with the efficiency of 93.58%. The results of the present study indicates that the SMSP can be successfully employed for the removal of Zn(II) ions from aqueous environment.

6

An alternative method to determine the diffusion coefficient for the shrinking core model

Kwiatkowska-Marks S., Wójcik M., Kopiński L.

Polish Journal of Chemical Technology

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2011

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Vol. 13, nr 2

54-56

EN

A new method to determine the effective diffusion coefficient of sorbate in sorbent granule based on the analytical solution of the shrinking core model (SCM) has been proposed. The experimental data presented by Lewandowski and Roe concerning the sorption of copper ions by alginate granules have been applied to compare the analytical and numerical methods. The results obtained by both methods are very close.

7

Application of shrinking core model to bioleaching of black shale particles

Szubert A., Łupiński M., Sadowski Z.

Physicochemical Problems of Mineral Processing

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2006

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Vol. 40

211-225

EN

Four size fractions of a black shale ore originating from the Lubin Copper Mine (Southwestern Poland) were leached in a small column using autotrophic bacteria (Acidithiobacillus ferrooxidans). The best results of bioleaching were obtained for the most fine fraction, where the copper recovery was 84%, and the surface area of the ore increased from 4.50 m2/g to 13.74 m2/g. Based on the shrinking core model, a new model describing bioleaching of the black shale type ore in a column is proposed. The model is based on assumption of dependence of copper recovery and surface area increase during the process.

PL

Cztery klasy ziarnowe rudy łupkowej, otrzymanej z kopalni Lubin (Polska Miedź S.A.), zostały poddane procesowi bioługowania w kolumnie. Do procesu bioługowania wykorzystano autotroficzne bakterie Acidithibacillus ferrooxidans. W wyniku procesu bioługowania odzyskano 84 % miedzi z najdrobniejszej frakcji rudy (2,5-1,6 mm). W trakcie procesu bioługowania nastąpił wyraźny wzrost wielkości powierzchni właściwej ługowanych ziaren mineralnych. Początkowa wartość rozwinięcia powierzchni wynosiła 4,50 m2/g a po procesie bioługowania osiągnęła wartość 13,74 m2/g. Opracowany został nowy model bioługowania rudy łupkowej w kolumnie. Nowy model bazuje na istniejącym i opisanym w literaturze modelu kurczącego się rdzenia. Nowy model poprawnie opisuje otrzymane wyniki eksperymentalne.