The aim of this project is development of efficient, sustainable and intensificative technology of extraction of gold from rebellious gold-arsenic raw materials and studying of influence of physical and chemical conditions and the basic technological parameters on the degree of gold extraction.
Status of researches. A significant number of gold-bearing ores in the world, including in Tajikistan, according to its mineral composition belong to the category of rebellious ores. Processing of rebellious gold ore is of great interest. One of the peculiarities of mineral composition of rebellious gold ore is the presence of nana-particles of gold. This is submicroscopic gold with sizes 1-100nm («the invisible things of gold»). Usually the kind of gold that meets in pyrite, arsenopyrite, marcasite. Therefore, data processing ores requires a combination of processes of enrichment and hydrometallurgy, often cyanidation. However, without opening the gold-bearing minerals ore gold cannot be removed. In practice, there are a number of methods for the processing of such ores, including oxidizing roasting, bacterial leaching of minerals etc., then data ores or concentrates are subjected to cyanidation. Cyanidation is a traditional method of leaching of gold, the duration of which due to low dissolved oxygen concentrations (3-5 mg/l) in the pulp is 24-48 hours. The increase in the concentration of dissolved oxygen is in proportion to the reduction in the duration of leaching. Another, but not less important problem of leaching is consumption of the main part of the dissolved oxygen to oxidation of iron sulphides during the processing of refractory sulfide ores and concentrates. Commonly leaching in autoclaves is recommended for this task. However, this method has a number of disadvantages: applicable only for the rich ores and concentrates, complicated apparatus design and management, energy-intensive and requires a trained specialists. From the ecological point of view the rebellious and particularly resistant ores are the object of high danger, that requires developing new technologies or improving existing ones. But it is necessary to provide the output of toxic and ecologically dangerous impurities in a secure form. Traditional technologies of extraction of precious metals on the plants are not sufficiently effective, as part of gold does not extract, passing in the refuses, and, in addition, the process is very time consuming, which is one of the reasons for the ineffectiveness of these technologies. Thus, for the decision of tasks on processing resistant and extremely resistant ores and concentrates it is need to develop effective, environmentally safe intensificative ways to not only increase of gold recovery, but also economically advantageous process to similar raw materials.
One of the ways to intensify the treatment of rebellious gold ores can be the development of technologies with the use of energy impact, in particular, of the hydro transmitter. In this regard, the most promising is the cyanide leaching with the use of hydro transmitters that provides intensification of the process due to increase of concentration of dissolved oxygen in the leaching solutions. In addition, the creation of new designs of the hydro transmitters of wide range of frequencies will lead to a thin grinding (abrasion) of the processed material. This will allow more fully reveal the subtle gold in minerals, which will eventually lead to the final increase in the extraction of gold to solution.
One of the main problems of the gold mining enterprises in processing of rebellious ores and concentrates is a high content of iron sulfides. It is established that iron sulphides presented by minerals of pyrite, marcasite and pyrrhotite, are relative to cyanide solutions and dissolved in them the oxygen of the most harmful substances. Feature of the behavior of iron sulfides when cyanidation is that in the presence of oxygen, these minerals are oxidized, interact with cyanide and increase its consumption. This leads to a sharp fall in the dissolution rate of gold due to lack of oxygen in the pulp as the oxygen contained in cyanide solutions uses for the oxidation of iron sulfides. In connection with this perspective may be a way to pre-alkali processing of pulp using hydro radiator that will not only to increase the concentration of dissolved oxygen in solution, but also to move up the iron into not interactive with cyanide forms.
Influence of the offered project on progress in the given area. As a result of performance of a complex of works will be developed basics intensificative technology of gold extraction from rebellious and particularly rebellious ores and concentrates with the use of hydro-acoustic devices of a new generation.
Competence of the project participants in this area. The project will be carried out at the Institute of Chemistry of the Academy of Sciences of the Republic of Tajikistan, where for many years researches are conducting in the field of flotation, hydrometallurgy, biotechnology, as evidenced by numerous publications and presentations at international conferences (The list of some publications is given in Supporting Information). 2 professors and 5 candidates of science (PhD on science) are among the project participants. They have extensive experience in the enrichment of ores of antimony, gold, copper, bismuth, lead, etc., and in terms of concentrates preparation by hydrometallurgical methods and also in construction of hydro acoustic generators.
Expected Results and Their Application. In the result of the project theoretical and experimental data on the technology of extraction of gold will be presented by efficient, environmentally safe and intensificative way in relation to the rebellious and particularly rebellious gold-enriched arsenic ores and concentrates. The developed technology with the use of hydro transmitters of new generation will promote the increase of the extraction of gold as a result of its opening in sulfides-carriers, and also the improvement of the technological parameters of the process due to increase of concentration of dissolved oxygen in leaching of gold. Besides, the developed technology will reduce the number of tanks for leaching, reduce the duration of leaching in 3-4 times, reduction in consumption of cyanide, increase the capacity of the plant is due to the intensification of the process cyanidation. The developed technology can be used in industrial processing of rebellious gold-bearing ores of Tajikistan and the similar ores of other countries.
Meeting ISTC Goals and Objectives. The project employed professionals (47%) that were previously occupied by the so-called weapons technology in the performance of government programs of the USSR, and who will participate in the project. Professors Zinchenko Z. and scientists Ismailova M., Tuymin I. took part in the project of ISTC N1598. Experience of specialists work in weapons technology is in area 2, 5 according to Appendix 2.The project itself has only peaceful purposes, and is consistent with the objectives of the ISTC.
During of the project execution will be established new and restored old contacts with leading research centers involved in processing of rebellious gold ores. In addition, studies will be presented at international conferences and symposia. This will facilitate the involvement of scientists in Tajikistan into the global scientific community.
Data on the volume of work. In the framework of the project will perform the following main stages of the work. Conducting mineralogical and chemical analysis of gold ores of Tajikistan:
- study of the chemical composition and determine the extent and causes of studied objects persevere;
- study of the chemical composition of the elements and components of the objects;
- study of mineralogical compositions studied objects, spectral investigation and study of the chemical compounds found minerals;
- laboratory study of the phase analysis of gold and based on definition of quantity of free, associated with harmful minerals gold.
Development of technological schemes of enrichment of ores with maximum recovery of useful components into concentrates. Study of hydrometallurgical processes of gold extraction from the studied objects. Investigation of physic-chemical bases of the hydro-acoustic radiation in leaching of gold from ores and concentrates:
- selection and justification of the design of transmitters with hydro-acoustic processing;
-study of the influence of the basic technological parameters on cyanide leaching with using hydro-acoustic radiation;
- investigation of the influence of the hydro-acoustic radiation on the degree of opening of gold;
- study of the kinetics of cyanide dissolution of gold in hydro-acoustic impact.
Physic-chemical bases of process of objects pre-alkali treatment with the use of hydro-acoustic transmitters:
- substantiation of the construction of the hydro-acoustic transmitter for the alkali processing;
- study of the influence of main technological parameters on the change in the concentration of dissolved oxygen in the process of alkaline processing;
- study of the influence of the provisional hydro-acoustic processing of objects on the degree of dissolution of iron minerals.
The development of well-stimulation of technological schemes for gold arsenic ores of Tajikistan. Presentation of the work results to the international scientific community.
The Role of Foreign Collaborators. Foreign collaborators are the important part for successful performance of the planned projects both estimation of fundamental and practical meaning of quality of performance of job and its results. A scientific - practical direction spent by them are rather close on character and meaning of the developed project. Within the framework of the uniform project and course of its performance it is obviously possible mutual information interchange, granting of the comments to the technical reports, sharing of the scientific equipment, rendering of assistance and granting of material support by the participant of the projects in visiting the international meetings, realization of joint working seminars. As collaborator of given project has shown the desire to emerge the head of the biohydrometallurgical laboratory from Institute of Environmental Geology and Geoengineering, Italy, Dr.Stefano Ubaldini.
Technical Approach and Methodology. Study of the chemical composition of the products will be done using a variety of methods, including visual and optical mineralogical studies, sieve methods, spectral semi quantitative, chemical and phase, neutron activation, assay tests, x-ray microanalysis.
In the process of enrichment of ores will be investigated nonionic surface-active substances that improve the recovery of precious metals.
With the purpose of intensification of the process of cyanide leaching of gold-containing refractory ores will be investigated acoustic radiators of new generation. Solutions of cyanidation will be analyzed by atomic absorption analysis.
