DEVELOPMENT OF RECOMMENDATIONS FOR CHEMICAL FIXATION OF SALT WASTE

ABSTRACT

The work proposes, based on the results of theoretical, laboratory, and pilot industrial studies of the process of fixing salt waste, to develop a method, recipe, project, and action plan for checking the quality of work and safety precautions for the implementation of a chemical method for fixing salt waste at the Tyubegatan potash deposit.

АННОТАЦИЯ

В работе предложен по результатам теоретических, лабораторных и опытно-промышленных исследований процесс закрепления солевых отходов. Разработан способ, рецептура, проект и план мероприятий проверки качества работы и техники безопасности осуществления химического способа закрепления солевых отходов Тюбегатанского калийного месторождения.

Keywords: salt dump, sludge, halite waste, salt waste consolidation, chemical process, solution, silicatization.

Ключевые слова: солеотвал, шлам, галитовый отход, закрепления солевых отходов, химический процесс, раствор, силикатизации.

Today, in the mine of the Tyubegatan mining complex, tailings management is associated with the construction of salt dumps from solid halite ore enrichment waste and the construction and operation of sludge storage facilities for storing liquid clay-salt sludge. With promising methods of ore enrichment, the amount of waste and the area it occupies is growing every year. A distinctive feature of halite and sludge waste is its high (up to 95%) content of easily soluble salts in water. When salt dumps and sludge storage areas are exposed to precipitation, sodium chloride brines form and accumulate, which leads to chemical contamination of soils. In addition, the reasons for the spread of salinity over large areas are wind and water erosion, as well as emissions of salt dust from the mining complex, which enhances the overall picture of salinization. When settling on the soil, salt emissions pollute the upper fertile layer. In addition to changes in the chemical composition of surface and groundwater, intense soil salinization is observed in areas affected by salt dumps, which causes a transformation in the species composition of vegetation. In this regard, methods of preventing and minimizing soil salinization by fixing the surface of salt waste with fixing solutions are becoming particularly relevant [1-9].

The physical and chemical process of fixing salt waste is based on good penetration of a silicate solution with low viscosity (2-3 MPa∙s) into the soil and on the rapid release of a silicic acid gel film cementing the salt waste due to the reaction of a sodium silicate solution with waste salts. Thus, the role of the second solution (silicate solution coagulant) in this case is played by the waste itself [1-6].

Pilot work was carried out on the dumps and tailings of the Tyubegatan potash deposit in order to clarify the main parameters of consolidation and development of work production technology [1-9].

To draw up a project for experimental work, an engineering-geological section of the site, absolute elevations of the ground surface, elevations of the upper and lower boundaries of consolidation, and groundwater levels were used [4].

The consumption rates of chemical reagents per 1 m³ of salt waste were presented in tabular form with a detailed indication of the reagents, their main characteristics, units of measurement, and volumes.

The volume, l, of the fixing solution per fill, was determined using the following formula [3]:

Q=n∙a∙l∙πr²=39∙6∙1∙3,14∙(0,5)²=184 l,

where: n - is soil porosity, %;

a – coefficient accepted by the condition: 4 – for each solution with two-solution silicatization, 12 – with one-solution silicatization, 10 – with resignation, 6-8 with gas silicatization;

l – insertion length, m;

r – direction of support, m.

When injecting a chemical solution into a salt waste, it is recommended to assign a flow rate depending on the filtration coefficient, taking into account the gelation time, through a perforated link 1 m long. The approximate flow rate was taken based on the following data:

Table 1.

Data

The volume, l, of the initial sodium silicate solution, which is necessary for the purpose of preparing the required volume of a solution of working concentration, is recommended to be determined by the formula [3]:

Q_и = [(ρ_p -1)/ (ρ_и – 1)] Q_р

where: ρ_p - is the density of the working concentration solution, g/cm³;

ρ_и – density of the initial sodium silicate solution, g/cm³;

Q_р – the volume of a solution of working concentration, l.

Calculation for 1 m³ of massif:

Q_и =  l

m_и - is the outcome of the mass of sodium silicate solution:

m_и =Q_и ∙ρ = 73,6∙1,49 = 109,7 kg

During the chemical fixation of salt waste, systematic monitoring is carried out at all stages and an assessment is given on the quality of the work performed.

Quality control of work on the chemical fixation of salt waste was divided into routine monitoring during the work and control determination of the results of silicification in accordance with current standards [1-5].

Current control during the process of silicatization or resignation at observation objects:

1) for the correct layout and sequence of processing wells in plan and stops in direction;

2) for lighting, temperature, silicate module, the presence of mechanical impurities, and the power of the activated solution;

3) for use, consumption, injection mode, and solution administration;

4) for the correct keeping of a logbook for the provision of salt waste, i.e. for compliance of changes with recorded actual data.

Control determinations of silicization results in order to assess their compliance with design implementation after completion of good work.

The quality of the salt waste supply was checked by drilling control wells with sampling for laboratory research and visual studies of the continuity of the supply.

The opening of control pits and control drilling began no earlier than 7 days after the completion of injection work.

The number of control wells is 3-5% of the total number of injection points. The number of pits was assigned at the rate of one per 5000 m3 of fixed salt waste. Control drilling was carried out using the core method. The diameter of the well is 127-150 mm. During drilling, a thorough description of the recovered salt waste samples and a visual assessment of the quality of fastening and the presence of silicate solution in the indicator (phenolphthalein).

When opening the pits, a description and selection of samples of the accompanying salt waste were drawn up and a report was drawn up with a detailed description and sketch of the nature of the contents and a visual assessment of its quality.

Compounds of fixed salt waste selected during drilling or from a pit are tested for tensile strength.

Reliability of fastening is ensured in two ways:

• in the mode of fixed salt waste on the indicator of influence (phenolphthalein), which was expressed in the method of soil coloring;

• according to the resistance of the fixed salt waste to the penetration of a pointed object under the influence of force.

The chemical soil stabilization project must contain:

1) situation plan, information on the main scope of work, as well as a list of the main equipment and materials used;

2) a project for the chemical fixation of salt waste, carried out at the pilot production site;

3) layout plan, sections, and necessary instructions for the work;

4) parameters of injection wells;

5) specification for the main technological and electrical equipment, as well as materials;

6) design diagrams of mortar units;

7) estimates, calculations, and unit prices;

8) scheme for organizing the work;

9) projects for organizing construction and work execution;

10) work schedules;

11) safety instructions;

12) data on transport, auxiliary devices, events, etc.;

13) instructions for determining and controlling quality, as well as accepting work performed.

The situational plan should show the location of the fastening object in connection with the production area, sources of energy, heat and water supply, connections to sewerage networks, transport accesses, and communication lines, as well as the features of the natural conditions of the work site area.

Data on the main volumes of work are presented in the form of a table, which is divided depending on the type of work into its component parts (main, pilot production, control, etc.). This table gives the names of the works and their brief characteristics, units of measurement, and volumes of work.

A list of main equipment and materials must be presented indicating their types, brands, GOST standards, and quantities required to complete the work

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