Batch solution mining using lithological displacement of an evaporite mineral stratum and mineral dissolution with stationary solvent

In an underground formation containing an evaporite mineral stratum comprising a water-soluble mineral selected from the group consisting of trona, nahcolite, wegscheiderite, and combinations thereof, said mineral stratum lying immediately above a water-insoluble stratum of a different composition, said formation comprising a defined parting interface between the two strata and above which is defined an overburden up to the ground surface, a method of solution mining of said evaporite stratum, comprising an initiation phase which comprises a lifting step (a), a soaking step (b), and an extraction step (c),

• wherein in step (a), a first solvent is injected at the parting interface to lift the evaporite stratum at a lifting hydraulic pressure greater than the overburden pressure, thereby forming a void at the interface and creating a mineral free-surface which comes in contact with said first solvent, wherein said first solvent comprises water or an unsaturated aqueous solution comprising sodium carbonate, sodium bicarbonate, sodium hydroxide, or combinations thereof;
• wherein in step (b), said first solvent is maintained stationary at said hydraulic pressure in the void to contact said mineral free-surface for a time sufficient to dissolve at least a portion of said mineral into said first solvent to form a first brine and a cavity with a new mineral free-surface, wherein said first brine comprises sodium carbonate, sodium bicarbonate, or combinations thereof;
• and
• wherein in step (c), at least a portion of said first brine is extracted from underground to the ground surface, and
• said method further comprising at least one exploitation phase,
• wherein the exploitation phase comprises a partial filling or filling step (d), a soaking step (e), and an extraction step (f),
• wherein in step (d), a second solvent is injected into the cavity obtained in step (b) to reach a target hydraulic pressure, wherein the second solvent comprises water or an unsaturated aqueous solution comprising sodium carbonate, sodium bicarbonate, sodium hydroxide, or combinations thereof, wherein the components of said second solvent are the same as or different than the components of said first solvent,
• wherein the target hydraulic pressure is
• the same as the lifting hydraulic pressure used in step (a),
• an intermediate lifting hydraulic pressure less than the lifting hydraulic pressure used in step (a) but greater than a hydrostatic head pressure at the depth at which the cavity is, or
• equal to or less than a hydrostatic head pressure at the depth at which the cavity is
• wherein in step (e), said second solvent is maintained stationary at said target hydraulic pressure in the cavity to contact said new mineral free-surface for a time sufficient to dissolve at least a portion of said mineral into said second solvent to form a second brine, wherein said second brine comprises sodium carbonate, sodium bicarbonate, or combinations thereof;
• and
• wherein in step (f), at least a portion of said second brine is extracted from underground to the ground surface;
• and
• wherein the time for dissolution in step (e) is sufficient to obtain a Total Alkali content in the second brine of at least 8 wt %.