Melnikov Institute for Comprehensive Exploitation of Mineral Resources, Russian Academy of Sciences, Moscow, Russia:

V. A. Chanturia, Chief Researcher, Academician of the Russian Academy of Sciences

A. S. Timofeev, Researcher, Candidate of Engineering Sciences

Mirny Polytechnic Institute (Branch), Ammosov North-Eastern Federal University, Mirny, Russia:
G. P. Dvoychenkova, Leading Researcher, Professor, Candidate of Engineering Sciences, dvoigp@mail.ru

Geological Exploration Company, PJSC ALROSA, Mirny, Russia:
Yu. A. Podkamennyi, Deputy Head of Department

Using a set of modern analytical and experimental research methods, the composition of diamondbearing kimberlite and placer materials as well as process slurry is analyzed. It is experimentally found that current and old tailings of diamond-bearing kimberlite mine and placer ore contain many secondary minerals and associates. High content of clayey minerals of the type of talc, talc saponite, chlorite saponite, Na saponite and X-ray amorphous phase is discovered. The test samples are characterized as calcite–dolomite formation with the increased content of quarts, while clayey fraction of this material is described as serpentine–carbonate association. Identity of grain size distribution and similarity of mineral components are found in the samples of the current and old tailings of diamond-bearing kimberlite mine and placers the complex composition which is one of the key factors to induce buildup of hydrophilic mineral impurities on the surface of diamond crystals during separation. The methods of optical microscopy, infrared spectroscopy and micro X-ray spectral analysis were used to study the surface of natural diamonds in interaction with the traced minerals. The integrated research shows that natural diamond surface with mineral impurities is nonuniform, features spreading films of calcium and magnesium carbonates and is covered by a mosaic of micro- and macro-size impurities of hydrophilic MG-silicate minerals, specifically, serpentine and talc with high iron mass fraction. It is found that the mechanism of formation and attachment of mineral impurities on the crystal surface is identical for altered kimberlite, diamond placer material as well as current and old tailings of diamond processing plant. From the analysis of thermodynamic calculation results, a hypothesis is proposed on feasible dissolution of mineral impurities on the surface of diamond crystals through modification of physical and chemical properties of liquid phase in ore slurry, reduction of concentration of bicarbonate ions and displacement of pH value to acid spectrum range down to wanted values.
The study was carried out in the framework of the Plan for R&D of the Research Institute for Comprehensive Exploitation of Mineral Resources, Russian Academy of Sciences, No. 0138-2014-0002, under the direction of Academician V. A. Chanturia.

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