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1SELECTIVE EXTRАCTION OF GOLD (III) BY INERT ORGАNIC SOLVENTS АND DETERMINАTION OF ITS METHYLENE BLUE (MB) DIRECTLY IN THE ORGАNIC
РHАSE
V.U. Otakuziyeva
Tashkent State Technical University named after Islam Karimov, E-mail: vazira.otakuz@mail.ru
Аbstrаct. A new highly selective, highly sensitive, accelerated and simple extraction photometric method for determining gold with MB directly in the organic phase has been elaborated. The developed method is tested on the analysis of production solutions of hydrometallurgical plants, concentrates and rocks without separation of accompanying elements. The developed method of extraction-photometric determination of gold with MB is recommended for the analysis of industrial solutions, waste water, ores, concentrates, rocks and other materials complex in terms of chemical composition without separation of the accompanying elements directly in the organic phase.
Key words. photometric method, gold, complex compounds, chloroform, gold extraction.
Introduction. Existing photometric and extraction-photometric methods for the determination of gold (III) for the use of organic dyes [1,2,3,4] are not very selective. Only a few works we can see investigates about minerals and receiving concentrates for extraction chloride of metal ions [5]. The results of the leaching of the tailings from the heap leaching section with the aim of extracting gold associated with sulfides are presented [6,7].Since the complexation of gold (III) with organic reagents happens during the water phase, the resulting ions often form complex colored compounds and conflict with the definition of gold. In the work [8] given general information on the chemical composition of ash and slag wastes and the content of valuable components of the most developed and used deposits in Kazakhstan and attractive from the point of view of extracting valuable materials from them.
Recently for increase of selectivity of methods for determination of elements a new method is applied - selective extraction of colorless complexes of elements by inert organic solvents, with the subsequent addition to the extract of organic dyes and their complexation directly in the organic phase [9,10].
This paper discusses a new selective, simple method based on selective extraction of gold chloride complex (III) with inert organic solvents and its complexation with MB directly in the organic phase.
Source solution of gold (III) with a concentration of 1MB/ml was prepared from the salt of chloride gold. Titer of solution was set by potentiometric titration with Mora salt [11]. Aqueous solution of MB was used.
The spectra of extracts of gold (III) and reagent complexes were shot on SP-26 spectrophotometer, £=1 see. Optical density of the solution was measured on the photoelectric colorimeter KPC-2. Experiments have shown that gold (III) from highly acidic solutions in the presence of chloride ions and dimethylformamide (DMFA) is well extracted by chloroform. In the absence of DMFA, gold (III) is not extracted. The study of gold extraction (III) by chloroform depending on the concentration of hydrogen ions, chloride ions and DMFA showed that the optimal conditions for gold extraction (III) are: 0.50 - 6.0 g ion/l for hydrogen ions; 0.06 - 2.5 g ion/l for chloride ions and 13 - 26 % (by volume) for DMFA, shaking duration of phases 5 - 10 s. At equal volumes of aqueous and organic phases extraction of gold (III) at a single extraction is 99.9 % and does not change to a ratio of 20:1 phase volume [12].
In these optimum conditions, the composition of the extractable gold chloride complex (III) by the equilibrium shift method has been determined [13]. For this purpose, the dependence of gold extraction (III) on concentration was studied: 1) hydrogen ions (0.030 - 0.96 g ion/l) at
constant concentrations of chloride ions (1.0 g ion/l), DMFA (20%) and ionic force (p=1) created by adding NaCl solution; 2) chloride ions (0.01 - 0.34 g ion/l), at constant concentrations of hydrogen ions (1.0 g ion/l), DMFA (20%) and ionic strength (^=1); 3) DMFA (5 - 13%), at constant concentrations of hydrogen ions (1.0 g ion/l), chloride ions (1.0 g ion/l) and ionic strength (p=1).
The concentration of gold (III) in the extract was determined by the photometric method with the MB reagent. For this purpose, an aqueous solution of MB was added to the extract and the phases in the organic phase were shaken. The resulting colored gold complex (III) with MB was photometrically photometrical relative to the blank experience extract prepared in a similar way. The data obtained are given in Tables 1-3 and Figures 1-3, shows that in bilogorithmic coordinates coordinates fgDAll-£gCH+, £gDAu - €gCcl_ , fgDAu - tgCDMFA
DMFA (where D is the distribution coefficient, C is the equilibrium concentration, moths) there is a straight-line dependence with tangent angles of straight lines equal to 1,4,3 respectively. Consequently, gold (III) is extracted by chloroform in the form of HAuCl4; the solvate number HAuCl4 in the extract is 3 [14].
Table 1
Determination of the number of H+-ions involved in the extraction of gold by _chloroform. AnP=0,57; cau=0,9m0-5 m._
C H+, mol A D igD -tgC,+
0.015 0,340 1,100 0,040 1,820
0,030 0,400 2,350 0,372 1,580
0,60 0,470 4,700 0,671 1,320
0,119 0,510 8,500 0,930 0,919
0,340 0,540 18,000 1,360 0,630
0,260 0,550 27,500 1,440 0,440
Figure 1 Determination of molar ratios of Au: H+ - ions by the equilibrium shift method during chloroform extraction, V0=10 ml I = 1 cm
Figure 2. Determination of molar Au: Cl-ratios by the equilibrium shift method during chloroform extraction, V0 =10 ml I = 1 cm.
Table 2
Determination of the number of chloride ions involved in the extraction of gold by
chloroform. Anp=0,57; CAu=0,9140" m.
CCi-, mol A D igD -igCa-
0,015 0,080 0,160 0,790 1,819
I K ;HCKA XAEAMA P 1
0,019 0,180 0,450 0,350 1,690
0,035 0,260 0,810 0,090 1,600
0,030 0,360 1,630 0,310 1,530
0,035 0,419 2,630 0,419 1,450
0,040 0,500 6,250 0,790 1,390
0,045 0,540 13,500 1,130 1,340
0,050 0,560 38,000 1,440 1,260
Table 3
Determination of the number of DMFA molecules involved in the extraction of gold by chloroform. Anp=0,57; CAu=0,9M0-5 m.
CDMFA j m°l A D igD -lgCDMFA
0,519 0,135 0,310 - 0,508 0,285
0,789 0,280 0,960 -0,0177 0,103
0,909 0,340 1,480 0,170 0,040
1,039 0,390 3,160 0,499 -0,016
1,169 0,440 3,380 0,530 -0,067
1,300 0,480 5,300 0,724 -0,113
Figure 3. Determination of Au: DMFA molar ratios by the equilibrium shift method during chloroform extraction.
Figure 4. Determination of the composition of the gold complex with MB method of balance shift.
To fully identify the mechanism of extraction of gold (III) studied the number of hydrated water molecules in the extract. For this purpose, 10 ml of a mixture containing 1 M HCl and 20% DMFA, 10 ml of chloroform and shaking for 5 - 10 seconds was added to 5 MB of gold (III). A blank solution without gold was prepared in a similar way (III). After complete separation of the aqueous phase extract, the extracts were poured into dry cylinders with grated plugs. Determination of water was carried out by the Fisher method [15] by amperometry titration. For this purpose, Fischer reagent from micro burette was poured to 1 ml of the test extract taken by the dispenser, the titer of which was determined in advance by water suspension. Under the action of the Fisher reagent the arrow of the galvanometer was shifted towards the
current increase and set constant at the end of titration. Knowing the Fisher reagent titer (T=0.0018 g/ml), the water content was determined by formula: g_H2o= T-V, (where V - is the volume of Fisher's reagent that went on hydrated water titration (V=0.101 ml), T - is the Fisher's reagent titer). The amount of hydrated water in chloroform extraction: gH2o = 0,0018 • 0,101 = 0,0001818 gr/ml = 0,1818 gr/l.
Given that the titration of the taken 5 MB of gold (III) and the volume of chloroform 10 ml we calculate the number of hydrated water molecules:
9E-:2D
3au a-au
0.1313 0.5
35,796 +
13
196.9
= 3,9777 4.
nH2a=M«2o
Consequently, during the extraction of gold (III) chloroform hydrate 4 water molecules. Considering this, the mechanism of extraction of gold (III) can be represented by an equation: AUC14 (b) + H(H20)4+ + 3 DMFA(B) ^ [H(H20)4 (DMFA)3]+ [AUC14]""(o).
Therefore, the gold chloride complex (III) in the presence of DMFA is extracted by the chloroform for the hydro-solvate mechanism [16].
After extraction of gold (III) chloroform in optimal conditions, separation of the aqueous phase of the addition to the extract of aqueous solution of MB and shaking phases for 10-15 seconds is complexing gold (III) with MB in the organic phase. The study showed that almost complete complex formation of gold (III) with MB in the chloroform occurs in the pH = 6 -10 range. The stability of the gold (III) extract has been studied depending on the volume of MB aqueous solution. It is found that the chloroform extract of gold (III) is stable to the ratio of water and organic phases of 1.5:1.0. Gold complex (III) with MB in the organic phase is stable for more than 3 days.
The influence of MB concentration on the completeness of gold complexation has been studied (III). For this purpose, to a constant amount of gold (III), after extraction in optimal conditions, added an increasing amount of MB and photometric. Experimental data showed that the full complex formation of gold (III) is achieved at 18-fold molar excess of MB (Table 4 and Fig. 4).
Table 4
Determination of the equilibrium composition of the gold complex with MB method of
balance shift. CAu =7,65 • 10-6 m, Anp=0,52
Cmb, M10-5 A D tflD [kompl]M106 [MB] M106 -tfl [MB]
1,357 0,430 4,777 0,679 6,319 7,255 5,140
1,630 0,440 5,500 0,740 6,470 9,819 5,010
1,900 0,450 6,419 0,808 6,619 13,385 4,910
2,172 0,460 7,619 0,880 6,760 14,950 4,819
3,358 0,480 12,000 1,079 7,060 25,530 4,600
4,344 0,500 25,000 1,297 7,360 36,085 4,450
The absorption spectra of gold (I II) complexes with MB and reagent MB are shown in
Figure 5.
As can be seen from Figure 5, the maximum light absorption of the complex with MB (Row1) is at 650 nm. The molar repayment ratio of the complex is 1.22-105. The Ber law is observed in the interval of 1-120 |ig of gold (III) in 10 ml of the extract. Reproducibility of definitions is in the range of 2-5%. There are three graded charts in the intervals of 10 - 10, 10 -60, 60 - 120 |ig of gold. Optical density of complexes was measured in cuvettes with thickness of 20, 10, 3 mm.
The determination of molar ratios of the components in the resulting gold (III) and MB complexes was carried out by the equilibrium shift method [8]. To determine the composition of the gold (III) complex with MB to chloroform extract containing a constant amount of gold (III)
(1,326 • 10-5 M, Апр = 0,7) were added 10 ml from 1,359 • 10-5 to 24,403 • 10-5 M aqueous solution of MB in the chloroform and shaken the phases 10-15 sec. The resulting painted gold complex (III) with MB was photometrically photometrical relative to the blank solution prepared in a similar way with the same amounts of reagent. From the tabular data (Table 4) we made a graph of dependence of CgD on -Cg[MB] (Fig. 5). 0,7 -|
0,6
0,5
0,4
0,3
0,2
0,1
0
580 600 620 640 660 680 700 • Row1 —•— Row2
Figure 5. Absorption spectra of gold complexes (III) with MB (Rowl) and MB reagent (Row2) in chloroform (CAu =0,51 • 10-5 M; V0=10 ml; I =1cm)
The tangent angle of the straight line on the graph shows that gold (III) in the chloroform interacts in a molar ratio of 1:1. Considering the mechanism of extraction of gold chloride complex (III) and the composition of complex compounds with MB, the reaction of complexation of gold (III) with the MB reagent in the organic phase can be presented in the following scheme: [H (H2O)4 (DMFA)3]+ [AuCl4]-(o) + PC1(b) ^ PAuCl4 + 3DMFA + HCl + H2O. Where the P - is the MB cation.
Methods for determining gold in pure solutions
The dividing funnel is filled with the analyzed solution containing 1.0-120 |ig of gold (III), 1 ml of concentrated hydrochloric acid is added to the dividing funnel and the volume of the solution is brought to 8 ml with water, 2 ml of DMFA, 10 ml of chloroform is added and 5 -10 s are shaken. The extract is washed with 10 ml of solution containing 1 M HCl and 20% DMFA, and 5-10 s are shaken. Then add 10 ml of 0.010% aqueous solution of MB to the extract and shake 10-15 sec. The resulting colored complex is filtered through filter paper into a cuvette and measured the optical density relative to the blank extract.
In industrial samples and minerals, gold is found in mixtures with many elements. In order to identify the possibility of determining gold from complex chemical samples was studied the influence of foreign ions in determining gold with MB. The method for determining gold in the presence of foreign ions is the same as for determining it in pure solutions, with the only difference being that certain amounts of foreign ions or compounds are preliminarily added to the determined solution and in some cases, if necessary, masking agents are added and the extract is washed once with a washing solution containing HCl and DMFA.
Under conditions of extraction of gold (III) partially extracted thallium ions (III) and antimony (V) and interfered with the definition. However, thallium (III) in chloroform extract with MB in the medium of 0.05 - 0.5 M of borax does not form a colored complex compound and its 5000-fold amount does not interfere with the definition of gold. In the presence of tungsten to prevent the deposition of tungsten acid and to eliminate the interfering effects of
antimony (V) previously added 0.01 - 0.5 g tartaric acid. Data on the definition of gold in the presence of foreign ions are given in Table 5 with a relative error within 2-5%.
Tаble 5
Determination of gold (III) with MB in the presence of foreign ions (10 ^g gold was
aken)
M M/Au M M/Au M M/Au M M/Au
Ag (I) 2000 Mn (II) 100000 Cr (III) 20000 W (VI) 20002
Ag (I) 15000 Cd (II) 80000 Ti (IV) 15000 Mo (VI) 15000
Pb (II) 2000 Hg (II) 10000 Sn (IV) 50000 Te (VI) 30000
Pb (II) 200003 Bi (III) 20000 Th (IV) 22000 Mn (VII) 1000
Zn (II) 50000 Fe (III) 30000 Pt (IV) 2000 Os (VIII) 200
Ca (II) 20000 Iu (III) 15000 Se (IV) 3000 NaF 5000
Ba (II) 20000 Al (III) 15000 Zr (IV) 15000 NO3" 6000
Cu (II) 20000 Ga (III) 10000 Sb (V) 150 PO4"3 2000
Ni (II) 30000 La (III) 20000 Sb (V) 30002 tartaric acid 100000
Co (II) 35000 Tl (III) 10001 As (V) 20000 citric 100000
Pd (II) 2000 Tl (III) 50004 U (VI) 10000 acid
Be (II) 2000 Tl (III) 100001 W (VI) 150 thionalide 10000
Where M - ion or compound; M/Au - allowable ratio to gold by weight; 1 - in the presence of 100 MB thionalide; 2 - in the presence of 0.5 g of tartaric acid; 3 - after heating the solution with sludge in a water bath for 2 - 3 minutes; 4 - when shaking the extract with aqueous solution of MB, containing 0.05 - 0.5 borax.
In order to find out the possibility of determining gold in various objects, we carried out the analysis of production solutions, (Table 6) concentrates and rocks (Table 7).
In determining the gold (III) in the production solutions are taken 1 - 2 ml of aliquot part of the solution and further analysis is carried out as in the analysis of gold from pure sol utions. The gold content is determined from the calibration chart.
Table 6
Determination of gold in production solutions (n = 4; p = 0.95)
Content of gold in the production solution, MB/l Found \ yj gold, MB/l Sr A* ±- ■ 100 X
1,60 1,55 0,0160 ± 0,039 ± 2,50
15,20 15,30 0,0094 ± 0,220 ± 1,50
45,00 45,50 0,0056 ± 0,410 ± 0,990
101,00 101,60 0,0075 ± 1,220 ± 1,20
142,50 142,30 0,0094 ± 2,134 ± 1,50
To determine the gold (III) in the concentrates and rocks calcined at 600 - 6500 C for 1.5 hours a canopy (10 - 20 g) is placed in a conical flask for 250 ml, 30-60 ml of a mixture of hydrochloric (p 1.19) and nitric (p 1.4) acids (3:1) and evaporated to wet salts. Then add 10 - 20 ml of the same mixture of acids and again evaporate to wet salts, then pour 30 - 40 ml of 1 M HCl and boil for 5 - 10 minutes. Cool the solution and filter it into a measuring flask for 50 or 100 ml, then dilute the filtrate 1 M HCl to the mark and determine the gold content from the aliquot of the solution.
Table 7
KHCKA XAEAMAP
Results of gold (III) determ^^on in concentrаtes аnd rocks аt chloroform extrаction
(n = 4; р = 0.95)
Sаmрle Contents, Аu gr/t Found Au QX gr/t Sr ±- ■ 100 X
Concentre 50,00 51,20 0,034 ± 2,780 ± 5,42
Concentre 37,50 96,50 0,022 ± 1,277 ± 3,50
Concentre 22,00 21,60 0,028 ± 0,972 ± 4,50
Breed 8,30 7,60 0,036 ± 0,441 ± 4,80
Breed 5,60 5,15 0,041 ± 0,334 ± 6,50
Discussion of results
Therefore, our research allows us to conclude that the low selectivity of metalloids definitions using basic dyes, as well as the use of other organic reagents in the complex formation in the aqueous phase is the main disadvantage of existing methods.
Our research has focused on ways to increase the selectivity and sensitivity of photometric definitions, as these analytical characteristics play an important role in the practice of analytical chemistry. We have investigated the conditions of selective extraction of the gold chloride complex in the presence of DMFA inert organic solvents and its determination directly in the organic phase without separation of the accompanying elements.
Researches have shown that gold (III) from a highly acidic environment is selectively extracted by chloroform in the presence of chloride ions and DMFA. At 5 - 10 second phase shaking gold (III) is extracted by 99.9% without changes to the ratio of phase volumes 20:1.
Under these optimal conditions, thallium (III), antimony (V) and tungsten (VI) are partially extracted together with gold and interfere with the definition. However, thallium, antimony, and tungsten interfere with the extraction by adding masking agents to the extraction mixture.
The research of substance of extracting gold chloride complex (III) in the extract has shown that the gold chloride complex (III) is extracted by the hydro-solvate mechanism. Gold chloride complexes (III) in the extract are stable for a long time and subject to the Beers law in a wide concentration range. The method is valuable also by the fact that after the extraction of gold in the organic phase there is a possibility of forming complexes with more sensitive organic reagents, which due to low selectivity have not received wide application.
Conclusions. The research resulted in the development of a new highly selective, accelerated and quick spectrophotometric extraction method for the determination of gold directly in the organic phase. It has been established that gold (III) is extracted by chloroform from a highly acidic medium in the presence of chloride ions and DMFA by the hydro-solvate mechanism. The influence of foreign ions that do not interfere with the definition of gold in large multiples has been studied. The developed method was tested on the analysis of production solutions, concentrates and rocks without separation of accompanying elements. The method is easy to perform, highly selective and rapid.
The developed method of extraction-spectrophotometric determination of gold is therefore suggested for the analysis of industrial solutions, wastewater, concentrates, ores, rocks and other materials with complex chemical composition without the separation of the corresponding elements directly in the organic phase.
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