Recycling prospects for saponite-containing water at 2 diamond processing plants in Arkhangelsk region , 3 Russia 4

The analysis of methods of cleaning and processing of saponite-bearing technogenic 17 waters of diamond mining enterprises of the Arkhangelsk region is carried out. The perspective of 18 the electrochemical separation method for extracting saponite from man-caused waters, providing 19 a targeted change in its structural-texture, physico-chemical and mechanical properties, is shown. 20 The possible directions of realization of saponite and products of its modification in various 21 branches of industry are considered. 22


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Developing of Lomonosov deposit in the Archangelsk diamond province, currently including 27 10 kimberlite pipes, to the depth allowing for quarry operations will require extracting of about 300 28 mln t of diamond-bearing ore and barren rock [1,2]. The rock of the deposit pipes is almost entirely 29 displaced by clay minerals, predominantly saponite, amounting to 90% in the vent facies [1].

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Saponite, belonging to smectite group minerals, is characterized by high physico-chemical 31 activity and low density in aqueous media owing to its tendency to hydrate. When in an aqueous 32 medium, saponite disperses forming a suspension, which creates difficulties both in operating of 33 tailing dumps and managing the closed water circulation at processing plants.

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In this regard, search activity, justification and effective process development techniques for 35 treatment and reprocessing saponite-containing man-caused waters from the diamond processing 36 plants have become the challenging objectives. They are determined by the necessity of developing 37 a qualitative water circulating system. All that will ensure both the advanced diamond recovery    The chemical composition of naturally occurring saponite is highly variable due to common 77 Fe 2+ , Fe 3+ and Al 3+ substitutions for Mg 2+ in the octahedral sheet, which are accompanied by partial 78 Al 3+ and Fe 3+ substitutions for Si 4+ in the tetrahedral sheet [8,9]

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Saponite is different from the other smectites as part of the negative tetrahedral charge is 83 balanced by substitution of octahedral Mg 2+ by trivalent cations, Al 3+ or Fe 3+ , i.e. the octahedral sheet 84 can to bears a positive charge. However, the tetrahedral charge, due to substitution of Si4+ by Al 3+ is 85 much greater and outbalances any possible positive octahedral charge [11].

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The mineral's properties are drastically affected by substitutions, their quantity and cation 87 kind. Moreover, the iron present in the mineral as an isomorphous impurity may vary its oxidation 88 degree in response to certain conditions, which leads to changing of the mineral's properties.

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Fairly often, the composition of natural saponite is heterogeneous and, similar to the rest of 90 smektites and other layered silicates, may contain fragments of other layered silicates, up to 91 forming of mixed-layer structures. Saponite is commonly found in association with 92 montmorillonite or talc [12][13][14]. According to the authors of [14], mixed-layered aggregates of this type have a greater surface area of up to 283 m 2 /g, and a high concentration of mesopores 94 comparable with quality sorbents.

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In order to obtain a chemically and phase-wise homogeneous composition, saponite is 96 synthesized to make controllable its properties, primarily the surface charge distribution [15][16][17].

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There is no evidence of studies of the sorption mechanism on natural saponite, but some 114 results have been reported on the sorption of saponite-containing products [27,28].

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Regarding the thermal properties, the Arkhangelsk saponite is close to smektite [10].

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Differences can be observed in the area of the second endothermic effect, which is attributable to 117 occupancy of the octahedral layer.

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The unique property of smektite crystals consisting in increasing or decreasing of the number 119 of water molecules between its layers from 0 to 4 layers/ , causing the basal distance to increase 120

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The experiments of the authors of [1,34]

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Compared to untreated clay minerals, the acid-activated ones acquire greater adsorption 307 capacity due to increased surface and pore volume. The removing is affected by pH, and the 308 quantity of adsorbed matter increases with pH growth until the ions begin to precipitate as 309 insoluble hydroxides at pH higher than 6.0. Adsorption the Cu(II) ions is very rapid at the onset of 310 the adsorbed substance-adsorbent interaction. The process kinetics is highly complicated and, 311 although the authors have applied different kinetic models, they failed to draw a definite 312 conclusion about the rate process mechanisms. It is highly probable, however, that the adsorption

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Invention [70] proposes a method for the production of a granular adsorbent featuring a high 378 hardness, water-resistance and good adsorbing efficiency by mixing a certain quantity of layered 379 silicate mineral with an alkali metal hydroxide, which is followed by pelletizing and calcination.

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The granular adsorbent is obtained by mixing 0.1 to 300 weight parts of a layered silicate mineral 381 with 100 weight parts of an alkali metal hydroxide, which is followed by pelletizing and calcinng.

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For instance, works [2,85,86] propose a method for pelletizing of iron-ore concentrates and 508 producing high-quality building materials.

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In works [87][88][89] it is proposed to utilize clays with saponite composition as binding agents in 510 manufacture of autoclave silicate materials.

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The authors of [90] have prepared a method for the production of building plaster by utilizing 512 natural minerals, including clays. Compared to conventional cement mixtures, the resulting 513 mixture is characterized by low fissuring, good acoustic absorption, and better adhesion and initial 514 strengths.

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Work [91] proposes a method for controlling the water-cement ratio in hardening concrete 516 mixture by adding a fine saponite-containing product made from kimberlite ore concentration 517 waste. The addition of a 7% saponite-containing material provided an almost two-fold increase in 518 the concrete strength and improving of the frost-resistance brand to F150.

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It has been proved that the thickened saponite-containing material can be recovered as ceramic

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The modified saponite-containing product has been used to produce high-brand ceramic 524 bricks with a compressive strength, within the sintering temperature range, of 800-1000 о С of 525

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It also seems attractive to continue researching the possibility of involving the saponite-528 containing concentrates in pellets manufacture and using the electrochemically obtained 529 concentrates as drilling water component due to the small size (less than 7 µm) of quartz particles 530 in the concentrate.

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Consequently, on the basis of the analyzed capacity, techniques of producing and saponite-533 containing waste recycling, which develop during processing and enrichment of the M.V.
Lomonosov kimberlite deposit, with allowance for their structure and mineral composition 535 investigation, we have come to the conclusion that the cryogenic treatment and electrochemical 536 separation are the most advanced techniques for the recycled water treatment at the processing 537 plants.

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The electrochemical separation promotes manufacture of modified saponite-containing 539 products, which are characterized by the elevated level of minerals belonging to smectite group, 540 decrease of mineral particles size, more compact structure and larger specific surface. All of these 541 characteristics presuppose wide possibilities for further manufacturing high-quality ceramic 542 materials and heavy-metal sorbents.

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Thus, the research reported in works [28,30,63,93] focused on the physical-technical, and 544 sorption properties of electrochemically modified saponite-containing products to estimate the 545 feasibility of converting them to high-quality ceramic items and heavy-metal sorbents. Having 546 examined the structure and mineral composition of electrochemically modified saponite -a waste 547 of circulating water from diamond-bearing kimberlite concentration, the authors were the first to 548 scientifically and experimentally validate some effective methods affording to manufacture high-549 quality ceramic materials with improved physical-mechanical and decorative properties and heavy-550 metal sorbents characterized by high cation-exchange capacity.

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Additionally, the following directions can be considered to be advanced:

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-applying of modified saponite-containing products for pelletizing;

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-manufacturing of drilling fluids (clay mud) due to low size of quartz crystal particles (less than 7 554 m) in the concentrate;