Underground sulfur smelting is a method of extracting sulfur from deposits by drilling wells and melting the sulfur using superheated water injected into the deposits. Hot water is injected through one pipe to melt the sulfur, which then flows down and is collected through a second perforated pipe before being pumped to the surface. This method is economically beneficial as it avoids the need to mine and process ore above ground. Wells are drilled and cased, then multiple concentrically arranged pipes are inserted to inject hot water, collect melted sulfur, and provide air lift assistance to transport the sulfur to the surface.

1. Underground sulfur smelting technology
• Underground sulfur smelting is a method of extracting sulfur through
wells by melting it with superheated water in place of occurrence and
delivering it to the surface in liquid form.

2. Technology features
• The mining process is based on heat exchange between the coolant
(hot water) supplied through the wells from the surface and the ore
massif.
• This method is economically beneficial, as it excludes the extraction
of ore, its delivery to the surface and subsequent enrichment, and
therefore gives the cheapest sulfur.
• USS is based on a lower melting point of elemental sulfur (112.8–119
°C) compared to host rocks (limestones), a high density relative to
water (1.8 t/m3), low viscosity and insolubility in water.

3. Schematic diagram of a production well
• 1 - casing string;
• 2 - annular grouting;
• 3, 4 and 5 - water supply,
sulfur and air columns;
• 6 - separation packer;
• 7, 8 - water and sulfur
perforations;
• 9 - stuffing box compensators.
Air
Hot
water
Sulfu
r

4. • Wells with a diameter of 400 mm are drilled
from the surface with conventional drilling rigs,
they are cased with pipes to a sulfur-containing
deposit and cemented.
• Then the well is drilled to the full capacity of the
deposit. Three concentrically arranged columns
of pipes are lowered into it: water supply,
sulfuric, air.
• There is a perforation (holes) in the lower part
of the water supply column, which is divided
into the upper one - water and the lower one -
sulfur with the help of a separating packer.
• Hot water enters the sulfur deposit through the
upper perforation, heats it up and melts the
sulfur.

5. Basic operations of USS technology
Operational
exploration
Drilling and well
preparation
Arrangement
Production of
working reagents
Mining work:
a) coolant injection
b) drainage
a) pressure relief in
the sulfur column
d) pumping and
transportation of
liquid sulfur
Purification and
discharge of
formation waters or
creation of a closed
water circulation
Reclamation

6. • At temperatures above 160 °C, the viscosity of sulfur increases rapidly, so water is
supplied to the well at 120–159 °C.Water at a pressure of 1.0–1.2 MPa is injected
through the upper water perforation of the pipe and enters the formation.
• Passing through cracks, pores and caverns, it melts sulfur, which flows down to the
bottom of the well and enters back into the pipe string (below the packer) through
the lower sulfur perforation. Molten sulfur, due to the pressure of the injected
water, rises above the level of the air pipe and is released to the surface by an
airlift.
Schematic diagram of the technological complex for the extraction of sulfur by US

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