Methodology for Determining Silver and Mercury in Ores by the PPN Method
Abstract Generated abstract
A procedure is presented for highly sensitive determination of silver and mercury in lead and zinc ores by stripping polarography with accumulation on a graphite electrode. Because simultaneous determination is limited by the silver to mercury ratio, the method uses dithizone extraction followed by separate re-extraction of mercury with potassium thiocyanate and silver with potassium bromide, while Trilon B and acidic conditions suppress copper interference and nitric acid decomposition minimizes gold interference. Application to mineral samples gave reported measurement errors for silver and mercury in lead and zinc sulfide matrices, with stated sensitivities of 4 x 10^-8 percent for silver and 4 x 10^-9 percent for mercury.
Full Text
METHOD FOR DETERMINING SILVER AND MERCURY IN ORES BY THE PPN METHOD
N. A. Kolpakova, A. I. Kartushinskaya
(Presented by the scientific seminar of KhTF)
Several methods for determining silver and mercury in ores and silicate rocks have been described in the literature [1–3]. However, the sensitivities of their determination either do not meet the requirements of modern geochemical analysis, or the procedures are lengthy and difficult to carry out.
The aim of the present work is to develop a simple and highly sensitive method for determining these elements using stripping polarography with accumulation on a graphite electrode.
The essence of this method has been described in a number of works [4–5].
From the studies we carried out, it was found that simultaneous determination of silver and mercury is possible only when their ratio in solution is 1:5. Therefore, to separate the elements we used extraction of silver and mercury with dithizone followed by re-extraction of mercury with 1 M KSCN, and of silver with 20% KBr. The polarographic determination of silver and mercury under these conditions is interfered with by gold and copper. To prevent extraction of copper, 0.1 N Trilon B solution is added to the solution and an acidic medium is created. Under these conditions copper is not extracted.
The conditions for decomposition of the sample were chosen so that gold from the rock would not pass into solution and would not interfere with the determination of silver and mercury.
In the course of developing the procedure, we analyzed lead and zinc ores. The apparatus for preparing the sample for the polarographic measurement is described in sufficient detail in work [4].
Decomposition of the sample was carried out with diluted (1:3) nitric acid at a temperature of 70–80°C. The amount of solvent was found experimentally.
On the basis of the investigations carried out, the following method is proposed for determining silver and mercury in lead-zinc ores.
Course of analysis
5 g of ground ore is dissolved at temperature \(t = 80^\circ\mathrm{C}\) in 20 ml of diluted 1:3 nitric acid. The solution is filtered to remove the undissolved residue of the sample. The filtrate is then evaporated at \(t = 80^\circ\mathrm{C}\) until the odor of acid has completely disappeared. The sample volume is brought to 50 ml; 5 ml of 1 N HNO\(_3\) and 5 ml of 0.1 N Trilon B are added. Silver and mercury are extracted three times with a 0.001% solution of dithizone in CCl\(_4\), in 2-ml portions for 2 min. The organic extracts are collected.
in a separatory funnel and washed several times with bidistillate. Then 5 ml of 1 M KSCN + 0.1 ml of 1 N TrB are added to the extract, and the silver is re-extracted for 2 minutes. The organic extract is transferred to a fourth separatory funnel, and the mercury is re-extracted with 5 ml of 20% KBr + 0.1 ml of 1 N TrB. The re-extracts are poured into beakers for polarography.
The polarographic conditions are given in Table 1.
The concentration of silver and mercury in the samples was determined by the method of additions and calculated by the formula given in article [6]. The results of analysis of a series of mineral samples are given in Table 1.
Table 1
Results of analysis of lead–zinc ores for silver and mercury by the PPN method
| No. | Main composition of sample | Conditions for carrying out the experiments | Found: a) Ag; b) Hg ×10⁷, % | Mean-square error | Confidence probability: Student coefficient | Confidence probability: relative error of a single measurement |
|---|---|---|---|---|---|---|
| a) | ||||||
| 1. | PbS | $\varphi_{\mathrm{e}}=-0.7\ \mathrm{V}$ rel. S.C.E. |
18.00 | 1.30 | 2.26 | 5.4% |
| 2. | ZnS | $\tau=1\text{–}3\ \mathrm{min.}$ background 1 M KSCN |
3.31 | 3.20 | 2.26 | 7.6% |
| 3. | PbS | $i=1\cdot10^{-9}\ \mathrm{a/mm}$ | 1.29 | 0.14 | 2.776 | 15% |
| b) | ||||||
| 1. | PbS | $\varphi_{\mathrm{e}}=-0.8\ \mathrm{V}$ rel. S.C.E. |
5.30 | 0.28 | 2.26 | 12% |
| 2. | ZnS | $i=2\cdot10^{-9}\ \mathrm{a/mm}$ $\tau=1\ \mathrm{min.}$ |
— | — | — | — |
| 3. | PbS | $i=1\cdot10^{-9}\ \mathrm{a/mm}$ | 0.27 | 0.16 | 2.26 | 13.4% |
The sensitivity of the method is, for silver, $4\times10^{-8}\%$, and for mercury, $4\times10^{-9}\%$.
LITERATURE
- RZh Khim. 11G70, 1963.
- Z. Babaev. Studies in the Field of Inorganic and Physical Chemistry. Baku, Academy of Sciences of the Azerbaijan SSR, 1966, pp. 3–8.
- A. A. Saukov, M. Kh. Aidinyan. Zavod. labor. No. 1, 1941.
- N. A. Kolpakova, A. G. Stromberg, A. G. Fedoseeva, E. M. Malkov. Geokhimiya (in press).
- A. I. Kartushinskaya, N. A. Kolpakova. Izv. TPI (in press).
- N. A. Kolpakova, A. A. Kaplin, G. M. Nemtinova. Zavod. laborator. (in press).