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1

Improved recovery of gold and silver from thiosulfate solution on activated carbon in presence of ammonium persulfate

Mahmoud Mohamed H. H., Awad Hesham M.

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 5

1271--1285

EN

Thiosulfate (TS) process for extraction of gold and silver is a promising alternative to the highly toxic cyanidation process. One of the main reasons caused limiting the practical application of the TS process is the poor recovery of gold and silver on the commonly used activated carbon (AC). Increasing amounts of TS ions greatly inhibited the adsorption of gold and silver from synthetic solutions. No adsorption was obtained when the TS concentration reached 0.8 M after 5 h. The adsorption efficiency from real leach liquor initially contained 0.2 M TS was as low as 40-50%, after a long time of 15 hours. We have suggested that the removal of the residual TS ions in leach liquor through an interaction with an oxidizing agent such as ammonium persulfate (APS) would improve the adsorption of gold and silver on AC. Increasing the APS concentrations from 0.0 M to 0.01 M drastically improved the gold adsorption efficiency from 5% to 85% after only 10 min. Almost 95% of both metals was adsorbed after 90 min. EDXRF chart confirmed the adsorption of gold and silver on AC. A process flowsheet was proposed for an integrated TS leaching and recovery of gold and silver from Al Amar tailing including adsorption on AC in presence of APS.

2

Gold recovery from refractory gold concentrates by pressure oxidation pre-treatment and thiosulfate leaching

Yu Li, Li Shimei, Liu Quanjun, Deng Jiushuai, Luo Bin, Liang Yuanqin, Zhao Liuchuang, Lai Hao

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

537--551

EN

Naturally, refractory gold is enclosed by sulfide minerals such as pyrite and arsenopyrite and a higher content of organic carbon, which results in difficulty in the recovery of gold. In this study, the flotation gold concentrate before and after pressure oxidation (POX) was analyzed. The analysis of the Eh-pH diagram revealed that pyrite/arsenopyrite would be dissolved in higher oxidation potential. Results of SEM-EDS showed that the surface of minerals became very rough and structure of some particles was destroyed after POX. The XRD measurement showed that pyrite was oxidized to jarosite, and gangue minerals such as quartz and organic carbon were hardly changed. The process of thiosulfate leaching of gold was designed and optimized according to Miscellaneous implemented by Response Surface Methodology (RSM). Based on the results of ANOVA, leaching model was significant. In leaching, [S2O32-] played an important role and the interactions between [S2O32-] and [Cu2+] were significant. The effect of [HA] was relatively weak. Optimum process parameters of the initial reagent concentration were 505.00 mM for [S2O32-], 34.77 mM for [Cu2+], and 0.50 mM for [HA]. Under these conditions, the Au extraction value was about 86.21%, which was significantly higher than that obtained with leaching directly.

3

Microanalysis study of Al-Amar rock and leaching behavior of its tailings for recovery of gold and silver

Mahmoud M. H. H., Awad H. M., Altalhi T.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 2

527--537

EN

Some Saudi gold ores, such as that at Al-Amar mine, suffer from low leaching efficiency using the toxic cyanidation process. Only about 60% of the gold and 26% of the silver in the feed ore can be extracted at 0.2% CN– after 24 h and the rest percentages of these metals remained in leaching residues (tailings). These tailings contained 1.1 ppm Au and 4.3 ppm Ag. Reprocessing of tailings serves both for economic and environmental reasons. A petrography analysis of the mineral constituents indicated that the rock samples consisted primarily of sphalerite, chalcopyrite, pyrite and galena in decreasing order of abundance. An electron probe microanalysis quantitatively showed that gold and silver were finely distributed in the grain boundaries and within sphalerite, chalcopyrite, pyrite, and quartz. The dissemination of gold and silver in these hard minerals may be the main reason for their low recovery by cyanidation. Open air roasting of the tailings can release amounts of the disseminated gold and silver which can be extracted during leaching with the harmless thiosulfate ion S2O32–. After studying the different parameters, we found that the maximum possible extraction of gold and silver from the tailings roasted for 2 h at 400°C reached about 50% at 0.2 M ammonium thiosulfate, 0.3 M ammonium hydroxide, solid–liquid ratio ½ for 24 h. These achievements represent a possible exploitation of the accumulated 1.65 million Mg tailing waste containing significant amounts of gold and silver valued at about $73 million.

4

Thiosulfate-copper-ammonia leaching of pure gold and pressure oxidized concentrate

Porvali A., Rintala L., Aromaa J., Kaartinen T., Forsen O., Lundstrom M.

Physicochemical Problems of Mineral Processing

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2017

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Vol. 53, iss. 2

1079--1091

EN

In this research cyanide-free leaching of pure gold and pressure oxidized refractory gold concentrate by thiosulfate-copper-ammonia solutions were examined. A quartz crystal microbalance (QCM) was used to study gold leaching as a factorial series where the best gold leaching rate (2.987 mg/(cm2∙h)) was achieved with a solution consisting of 0.2 M (NH4)2S2O3, 1.2 M NH3, 0.01 M CuSO4 and 0.4 M Na2SO4. Temperature had the greatest effect on the gold leaching rate. An increase in thiosulfate concentration (0.1–0.2 M) increased gold dissolution. The combined effect of temperature and ammonia concentration had a statistically significant effect on the gold leaching rate at 0.1 M M2S2O3. Combination of applied potential and NH3:S2O3 ratio had a statistically significant effect on the gold leaching rate at 0.2 M M2S2O3. An increase in applied potential decreased the gold dissolution rate at low ammonia concentrations but increased it at high concentrations. A pressure oxidized gold concentrate was leached for 6 hours in the batch reactor leaching experiments. The effect of rotative velocity (1.26–1.56 m/s) and slurry density (10–30 wt%) was investigated at the following leaching parameters: 0.2 M Na2S2O3, 0.6 M NH3, 0.01 M CuSO4, 0.4 M Na2SO4. Lower slurry density (10 wt%) resulted in a higher Au leaching efficiency. An increase in the rotation rate did not have an effect on the final Au leaching recovery. The best Au leaching efficiency (89%) was achieved with 590 rpm mixing, 1.56 m/s rotative velocity and 10 wt% slurry density.

5

Gold leching from a Saudi ore by the nonpolluting thiosulfate process

Mahmoud M. H. H., Awad H. M., Elhabib O. A.

Physicochemical Problems of Mineral Processing

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2015

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Vol. 51, iss. 1

59--72

EN

In all working Saudi gold mines, ores are treated using the hazardous cyanidation process. Some Saudi gold ores, such as Al-Amar, is known to be refractory to cyanidation. In this work, we have examined the extraction of gold from Al-Amar gold ore by the much environmentally safer and efficient thiosulfate process. The run of mine (ROM) and carbon-in-leach (CIL) feed, that is obtained after separation of copper concentrate from ROM, samples were found to contain 6.5 and 3.6 ppm gold, respectively. The mineralogical microscopic investigations of ROM samples confirmed that fine gold specks were scattered and encapsulated inside sulfide or quartz base minerals. This could explain the expected reason of the difficult leaching of gold by cyanidation. The X-ray diffraction analysis showed that the CIL feed contained quartz, pyrite, sphalerite and chlorite minerals. After detailed leaching studies of CIL feed, almost 70% of gold could be extracted at 0.2 M ammonium thiosulfate and 0.3 M ammonium hydroxide after 24 h. Addition of copper(II) as <0.2 mM only slightly enhanced the gold leaching in the ammoniacal thiosulfate solution. Gold leaching drastically decreased as the concentration of copper(II) increased 0.2 mM due to the degradation of S2O3²¯.

6

Kinetics and Mechanism of the Redox Reaction Between Pt(IV) Complex Ions and Sodium Thiosulfate in Aqueous Solution. Part II: Neutral and Alkaline Solution

Pacławski K., Piwowońska J.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 4

1421--1426

EN

In this work, spectrophotometric studies on the kinetics and mechanism of the reaction between [PtCl6]2- complex ions and sodium thiosulfate, in neutral (pH = 7) and alkaline (p = 12) solution, were carried out. Applying different conditions, the influence of initial concentrations of reductant and platinum(IV) complex ions as well as the influence of temperature and ionic strength on the rate constant, was experimentally determined. From the obtained results, the molecularity, the order and the value of enthalpy and entropy of activation of the reaction, were experimentally determined. It was found that in both cases the reduction reaction is relatively slow and in the studied conditions the second-order rate constant changes from 2.92 : 10-2 to 0.40 M-1:s-1 at pH = 7, and from 3.84 : 10-2 to 1.55 M-1s-1 at pH = 12. Additionally, depending on the pH, different mechanism of the reaction is present. However, regardless on the studied system the only platinum(II) chloride complex ions are the final product of the redox reaction.

PL

W pracy, przedstawiono wyniki badań spektrofotometrycznych nad kinetyką i mechanizmem reakcji pomiędzy jonami kompleksowymi [PtCl6]2- i tiosiarczanem sodu, w roztworze obojętnym (pH = 7) i zasadowym (pH = 12). Stosując różne warunki doświadczalne, wyznaczono wpływ stężenia początkowego reduktora oraz stężenia jonów kompleksowych platyny(IV), jak również wpływ temperatury oraz siły jonowej na wartość stałej szybkości reakcji. Na podstawie otrzymanych danych, wyznaczono cząsteczkowość, rząd oraz entalpie i entropie reakcji. Wykazano, że w obydwu przypadkach reakcja redukcji jest stosunkowo wolna. W badanych warunkach wartość drugorzędowej stałej szybkości reakcji ulega zmianie od 2.92· 10-2 do 0.40 M-1:s-1 w roztworze o pH = 7, oraz z 3.84 · 10-2 do 1.55 M-1s-1w roztworze o pH = 12. Dodatkowo, w zależności od pH roztworu, ulega zmianie mechanizm badanej reakcji. Jednakże, bez względu na zastosowane warunki pH, produktem końcowym jest zawsze chlorkowy kompleks platyny(II).

7

Kinetics and Mechanism of the Redox Reaction Between Pt(IV) Chloride Complex Ions and Sodium Thiosulfate in Aqueous Solution. Part I: Acidic Solution

Pacławski K., Piwowońska J.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 4

1413--1420

EN

In this work, spectrophotometric studies of the kinetics and mechanism of reaction between [PtCl4]2- complex ions and sodium thiosulfate, were carried out. The influence of different conditions, such as: initial concentrations of reductant and platinum(IV) complex ions, ionic strength, pH and temperature on the rate constant, was experimentally determined. From the obtained results, the molecularity of the first elementary step, value of the enthalpy and entropy of activation in Eyring equation as well as corresponding rate equation, were experimentally determined. It was found that the reaction is relatively slow and leads to the S, Pt and PtS colloids formation. The best conditions for solid phase formation containing Pt are at pH = 5.

PL

W pracy przedstawiono wyniki badań spektrofotometrycznych kinetyki i mechanizmu reakcji jonów kompleksowych [PtCl4]2- z tiosiarczanem sodu. Doświadczalnie określono wpływ różnych czynników na stałą szybkości reakcji, tj.: stężenia początkowego reagentów, siły jonowej, pH oraz temperatury. Na podstawie otrzymanych wyników wyznaczono cząsteczkowość pierwszego etapu elementarnego reakcji, wartości entalpii i entropii aktywacji reakcji oraz równanie kinetyczne. Wykazano, że reakcja jest stosunkowo wolna i prowadzi do powstania koloidu złożonego z siarki, platyny oraz siarczku platyny (PtS). Najlepsze warunki do wytrącania koloidu zawierającego Pt to pH = 5.

8

Zagrożenie bezpieczeństwa w procesie wytwarzania i przechowywania płynnych nawozów azotowo-siarkowych

Zdunek A., Możeński C., Biskupski A., Bielski P.

Przemysł Chemiczny

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2013

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T. 92, nr 12

2192-2197

PL

Przedstawiono wyniki badań nad zagrożeniem bezpieczeństwa w procesie wytwarzania i przechowywania nawozów płynnych (roztwory saletrzano-mocznikowe (RSM)) z dodatkiem siarki w postaci tiosiarczanów amonu, potasu i sodu. Badania wykonano za pomocą metody różnicowej i wagowej analizy termicznej (DTA -TG). Analizie poddano każdy z tiosiarczanów, a następnie układy złożone z azotanu amonu i tiosiarczanów, azotanu amonu, mocznika i tiosiarczanu oraz z azotanu amonu, mocznika, tiosiarczanu i wody. Badane tiosiarczany charakteryzują się zróżnicowaną stabilnością termiczną. W stosunku do wszystkich trzech badanych tiosiarczanów, nie stwierdzono zagrożenia bezpieczeństwa procesu wytwarzania i przechowywania nawozów RSM z dodatkiem tych tiosiarczanów.

EN

Aq. solns. of NH4NO3, urea and NH4, K and Na thiosulfates as well as their mixts. were studied by thermogravimetry and differential thermal anal. to det. the mass loss and exothermal effects at elevated temp. (up to 500°C). (NH4)2S2O3 showed the lowest thermal stability. Addn. of urea resulted in increasing the thermal stability of the soln. of NH4NO3 hazard during storage of the liq. NH4NO3-contg. fertilizers was obsd.

9

Przemiany chemiczne i biochemiczne wpływające na znaczne obniżenie odczynu ścieków w zakładowej oczyszczalni ścieków koksowniczych

Wiszniowski J., Owczorz H., Felis E.

Przemysł Chemiczny

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2012

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T. 91, nr 10

2033-2037

PL

Określono czynniki, które w znaczący sposób mogą wpływać na obniżenie odczynu ścieków koksowniczych podczas procesu biologicznego oczyszczania. Badania wykazały, że główną przyczyną drastycznego obniżenia odczynu medium podczas procesu oczyszczania są przemiany związków siarki, których obecność została potwierdzona w ściekach koksowniczych. Procesem, który w zasadniczy sposób wpływał na zmianę odczynu badanego medium był proces biochemicznego utleniania tiosiarczanów. Dodatkowo, na podstawie przeprowadzonych testów, można postawić tezę, że osad czynny pobrany do badań z bioreaktorów zakładowej oczyszczalni ścieków nie wykazywał aktywności nitryfikacyjnej.

EN

Cokery wastewater was studied for alky., phenols, phosphate P, ammonium, nitrite and nitrate N, cyanides, rhodanides, thiosulfates, sulfates, org. C and pH changes during storage for 48 h optionally under aeration, in presence of activated sludge and after addn. of Na₂S₂O₃, NH₄Cl and/or KCN. A decrease in pH was observed because of the biochem. oxidn. of thiosulfates to H₂SO₄. The activated sludge obtained from the cokery wastewater treatment plant did not show any nitrifying activity.

10

Determination of microamounts of sulfides and thiosulfates present together by means of induced iodine-azide reaction

Kurzawa J., Krzymińska A.

Chemia Analityczna

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2004

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Vol. 49, No. 4

569-576

EN

The induced iodine-azide reaction was applied to the titrimetric codetermination of microamounts of thiosulfates and sulfides. In one part of the sample the iodine consumed in the reaction induced by both inductors was determined. From the second sample one removed sulfides quantitatively by expelling H2S with N2 at pH 5. Alternative method of the removal of sulfides was based on their precipitation with zinc carbonate hydroxide suspension. After that the iodine consumed by the remaining thiosulfates was determined. From these two determinations the amount of both compounds was estimated. The method was applied to the determination of thiosulfates and sulfides in their mixtures and to the investigation of the stability of the prepared sulfide solutions and natural spring water containing sulfides. The proposed method allows one to determine both compounds at the concentration as low as 0.4 mmol L-1 with standard deviation š0.02.

PL

Opracowano metodę współ oznaczania siarczków i tiosiarczanów za pomocą indukowanej reakcji jodo-azydkowej. W jednej próbce oznaczono ilość jodu zużywanego w reakcji indukowanej łącznie przez oba związki. W drugiej próbce oznaczono ilość jodu zużywanego przez sam tiosiarczan po wcześniejszym ilościowym usunięciu siarczków przez wyparcie H(2)S za pomocą N(2), z roztworu o pH 5. Alternatywna metoda usunięcia siarczków polegała na ich wytrąceniu za pomocą zawiesiny węglanu sodu i octanu cynku. W oparciu o te dwa pomiary oznaczano ilość obu induktorów. Metodę zastosowano do oznaczania siarczków i tiosiarczanów w mieszaninie, badania trwałości rozcieńczonych roztworów siarczków oraz siarkowodorowych wód źródlanych. Metoda umożliwia oznaczanie obu związków począwszy od stężenia 0.4 mmol L(-1) z odchyleniem standardowym š0.02.

11

Iodimetric determination of tetrathionate and simultaneous determination of thiosulfate and tetrathionate

Ciesielski W., Żłobińska U., Krenc A.

Chemia Analityczna

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2001

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Vol. 46, No. 3

397-401

EN

The method of iodimetric determination of tetrathionate and simultaneous determination of thiosulfate and tetrathionate in one sample is described. Tetrathionate in alkaline medium (c(NaOH) = 5 mol 1(-1) is stoichiometrically converted into thiosulfate and sulfite, which react with iodine. In the volumetric titration with the potentiometric end-point detection the determination range is 10-800 umol for tetrathionate. In the first stage simultaneous determination of thiosulfate and tetrathionate, thiosufhate is oxidized in neutral medium with iodine to tetrathionate. In the second stage the total content of tetrathionate in alkaline medium is iodimetrically determined. The proposed method allows the determination of both compounds in the range from 30 to 400 umol in a sample with relative accuracy š1%.

PL

Opracowano metodę jodymetrycznego oznaczania czterotionianu oraz współoznaczania tiosiarczanu i czterotionianu w jednej próbce. Czterotionian w środowisku zasadowym (c(NaOH) = 5 mol 1(-1) jest stechiometrycznie przekształcany w tiosiarczan i siarczyn, które reagują z jodem. W miareczkowaniu objętościowym z potencjometryczną detekcją punktu końcowego oznaczono 10-800 umoli czterotionianu. Przy współoznaczaniu tiosiarczanu i czterotionianu w pierwszym etapie wykorzystano reakcję utleniania tiosiarczanu do czterotionianu jodem w środowisku obojętnym. W drugim etapie oznaczano jodometrycznie w środowisku zasadowym całkowitą zawartość czterotionianu. Współoznaczanie przeprowadzano w zakresie 30—400 umoli obydwu związków w próbce z dokładnością 1%.