In the laboratory, the wet chemical method is used to determine the amount of elements in the samples and it is classified into two groups: classical and instrumental. In the classical method, the sample digested in a suitable solvent and then the solution obtained from the sample digestion is titrated to determine the amount of each element in the solution using its appropriate reagent.
In instrumental method, the amount of the element in the digested solution is determined with a device. in this method, disturbing elements do not interfere with the assay measurement, therefor it is possible to measure infinitesimal amounts of the element in the mineral. Spectrophotometer, atomic absorption spectrophotometer and ICP can be mentioned among the most important instruments used in wet chemical method.
Having laboratories equipped with appropriate tools and cooperating with modern laboratories of Science and Technology Park of Semnan province, Shahrood University of Technology and Shahrood Islamic Azad University, this company performs chemical analyzes to perform various types of digestion to measure different elements or minerals. Below are introduced some of the most widely used digestion tests that are carried out in the wet chemistry laboratory of Kani Fan Avaran Shahvar Company.
1-Digestion tests
1-1- Cyanide digestion
Gold and silver are often found together in nature, and generally most processes used to recover one of these elements also recover the other. Cyanide is one of the most widely used solvents to digest gold and silver from their ores, and cyanide digestion in this laboratory is performed with the aim of measuring elements soluble in cyanide solvent and also measuring the cyanidation rate of elements in terms of a process to recover them.
2-1- Acid digestion
The digestion process of different elements and their different phases is performed in different acids. For example, sulfuric acid is used for copper digestion in the oxide phase, but it cannot be used for lead in the oxide phase under the same conditions. Therefore, for different species, the digestion process should be designed with their own appropriate solvent, in such a way that sometimes a combination of several acids is used for digestion, and only one acid is used for some elements. Of course, other effective parameters in digestion such as concentration and temperature are also carefully considered in this collection and will be designed and applied according to the mineral substance.
3-1- Ammonia digestion
Ammonia solvent is used for digestion and measurement of copper, silver, gold, cadmium, cobalt, nickel, palladium, zinc, lead and mercury elements in metallic and non-sulfide phases.
4-1- Aqua regia digestion
This digestion is used for dissolution of metal sulfides, most sulfates, carbonates, phosphates, organically bonded metals, gold, platinum, palladium, tellurides, selenides, and arsenide. Some silicates and aluminosilicates are partially digested by aquaria, but most remain undissolved.
5-1- four-acid digestion
In four-acid digestion method, a combination of nitric acid, perchloric acid, hydrofluoric acid and in the last step hydrochloric acid are used. This method dissolves most silicate and oxide minerals and the recovery percentage of minerals and analytes is very high. In this method, elements that are generally volatile such as arsenic, selenium, antimony, tellurium and thallium are also digested and their loss is minimized. The digestion temperature in this method is high and therefore not suitable for mercury.
2-Assaying
1-2- transition metals
In the laboratory, these elements are first digested with a suitable solvent, and then the final solution is tested using an atomic absorption or ICP-MS. In particular, silver alloys are first digested in nitric acid and then measured by the volumetric (potentiometric) method. Titrations performed with a potentiometer are called potentiometric titrations. In this method, the potential changes of the detector electrode compared to the reference electrode are measured for increasing certain volumes of the titrant.
2-2- Metalloid
Metalloids are seven elements that are between metals and non-metals and are placed in groups 13, 14, 15, 16 and 17 of the periodic table. These metals are in the form of a diagonal line from boron to statin, the elements in the upper and left side of this line show the behavior of non-metals, and the elements in the lower and right side of this line have metallic behavior. Metalloids in the periodic table include boron, silicon, germanium, arsenic, antimony, trillium and polonium. In the laboratory, these elements are first digested with a suitable solvent, and then the final solution is tested using an atomic absorption or ICP-MS.
3-2-Alkali and alkaline earth metals
Alkali metals include lithium, sodium, potassium, rubidium, cesium and francium. These elements together with hydrogen form group I of the periodic table of elements. Alkaline earth metals are metals that are in group II of the periodic table. Six elements in this group are beryllium, magnesium, calcium, strontium, barium and radium. Alkaline earth metals are not as reactive as alkali metals. However, they are more reactive than other elements of the periodic table. Alkali and alkaline earth metals are first digested in a suitable solvent and then, they are graded with the atomic absorption spectrophotometer, ICP-MS or ICP-OES.
4-2- rare earth elements
Rare earth elements include 17 metal elements in the periodic table, 15 of which are in the lanthanide group, and the other 2 elements, namely scandium (Sc) and yttrium (Y), are from the first group of intermediates. Because these elements are rare in the earth’s crust, they are also called Rare-Earth Element or REE. These elements are divided into light (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd) and heavy (Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc) according to their application, production rate and physical and chemical similarities. Scandium and yttrium are not among the lanthanides, but they are considered rare earth elements, because they exist in mineral deposits similar to lanthanides and have similar chemical properties to this group. These elements are first digested with several appropriate acid steps, and then the final solution is analyzed using an ICP-MS.
3- Assay measurement of commonly used metals
In general, the amount of almost all mineral compounds and elements can be determined using the wet chemical method, but in the industry, as well as in this company, the measurement of the following items is usually done by the wet chemical:
1-3- Copper
In the laboratory, the assaying of copper is done with great accuracy, and the methods of copper analysis are different according to its phase (oxidic, sulphide, free, etc.). Oxidized samples are digested with sulfuric acid under suitable pH and temperature conditions, and then they can be assayed by titration, atomic absorption, or ICP. For copper sulfide, first the sample is digested in Aqua regia and then its grade is measured by titration methods, atomic absorption or ICP. Also, it should be mentioned that for the first time in Iran, Kani Fan Avaran Shahvar Company is able to provide native copper digestion and measurement along with oxide and sulfide phases in mineral samples.
2-3- Lead and zinc
Lead and zinc are usually found together in nature due to the same depositional conditions. The ratio of zinc to lead metal in ore is usually from five to one to two to one. Depending on the type of mineralization and assay, these elements require more complex methods for dissolution, most of which are carried out in this laboratory.
3-3- Precious metals
Precious metals such as gold, silver, platinum, palladium and rhodium are present in very small amounts in the soil. There are different methods for digesting these metals. The choice of digestion method depends on many parameters such as grade, type of precious metal in the soil, type of rock and minerals in the soil, etc. Since the concentration of precious metals in soil is very low (about a few grams to several tens of grams per ton), their accurate measurement in soil is very important.
The wet chemical method is a suitable method to determine the amount of precious metals. Using this method, it is possible to quickly determine whether there is a precious metal in the soil or the desired sample or not. This work helps if there is no precious metal in the soil or the sample, or if its amount is very low, we don’t need to measure the amount of these metals any more, thus saving time and money. Now, if the amount of these metals is significant, their amount can be obtained with proper accuracy by using the wet chemical method.
Different methods are used to analyze gold in minerals, which are different according to the grade of gold in different minerals. If the concentration of gold in the ore is low, the XRF method is used, but this method only shows whether gold is present in the sample or not, and the method is not accurate and quantitative. More accurate methods for low gold concentration are Fire Assay and Aqua Regia methods. First, acid digestion is performed for minerals, to determine the highest grade of gold after acid digestion, chemical assaying methods such as Aqua regia and Fire Assay are used, and then using ICP-OES, the amount of iron, aluminum, sulfur and arsenic in the sample is Determined.
Aqua regia is a mixture of nitric acid and hydrochloric acid, which affects the structure of the sample and dissolves the gold in it. In this method, gold is absorbed by DIBK and then measured by an atomic absorption or ICP.
4-3-Fe-metal, sponge iron and bivalent and trivalent iron
Sponge iron is obtained from the direct reduction of iron ore. The appearance of sponge iron is in the form of spherical and porous pieces, which is why it is called sponge iron. The measurement of metallic or reduced iron (Fe-Metal) in sponge iron samples is done with high precision in the chemical laboratory of this company.
Also, in some mineral samples, iron exists in divalent and trivalent forms, and the sum of these two is called total iron concentration. After dissolving in hydrochloric acid, total iron is titrated with potassium dichromate standard solution and its value is calculated. In addition to the titration method, the concentration of iron in liquid samples is also determined by the atomic absorption spectrophotometry.
In some mineral and iron ore samples, in addition to the total iron concentration, the amount of divalent iron should also be measured separately, and the most common methods for determining the concentration of divalent iron are titration and atomic absorption. In the titration method, divalent iron is digested in two steps with appropriate acids and then titrated with standard potassium dichromate solution and its assay is calculated. Also, due to the instability of trivalent iron, for sample analysis, trivalent iron is first reduced to divalent iron and then it is carried out in the previous method.