Rock salt. His­to­ry, extrac­tion, and appli­ca­tion

Rock salt is an impor­tant min­er­al resource that is wide­ly used in the food, chem­i­cal, agri­cul­tur­al, and oth­er indus­tries. In Ukraine, it is mined from salt-bear­ing basins that formed mil­lions of years ago. The main deposits are con­cen­trat­ed in the Donet­sk, Dnipro-Donet­sk, Zakarpat­tia, Pre­carpathi­an, Pre­do­brudzhyn­skyi, and Black Sea basins. Ukraine ranks third among East­ern Euro­pean coun­tries in terms of rock salt reserves, which allows it to active­ly export this resource.

Rock salt is includ­ed in the list of min­er­als of nation­al impor­tance approved by Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine No. 827 of Decem­ber 12, 1994, as a chem­i­cal raw mate­r­i­al.

Physical and chemical properties of rock salt

Rock salt, or halite (NaCl), is one of the most com­mon min­er­als on Earth. It belongs to the halide class and is formed by the nat­ur­al evap­o­ra­tion of sea, lake, or under­ground water. Its phys­i­cal and chem­i­cal prop­er­ties make it indis­pens­able in many areas of life and indus­try.

This min­er­al has a cubic crys­tal struc­ture, which allows its gran­ules to be eas­i­ly split along cer­tain planes. Rock salt dis­solves eas­i­ly in water due to its ion­ic nature — sodi­um and chlo­rine form a strong elec­tro­sta­t­ic bond, which is bro­ken by the action of polar water mol­e­cules. Dis­so­lu­tion is accom­pa­nied by heat absorp­tion, which is why salt solu­tions have a cool­ing effect. It is this prop­er­ty that is used in refrig­er­a­tion.

In appear­ance, halite can be water-trans­par­ent or col­ored — gray, brown, red, pink, and oth­er shades. This is due to the pres­ence of impu­ri­ties of clay, iron oxides, organ­ic com­pounds, and oth­er min­er­als. A char­ac­ter­is­tic fea­ture is its salty taste, which is explained by the acti­va­tion of recep­tors on the tongue by ion­ic com­pounds.

The genesis of rock salt

The gen­e­sis of rock salt is asso­ci­at­ed with the nat­ur­al process­es of water evap­o­ra­tion in closed sea basins, lakes, or lagoons. Over mil­lions of years, under the influ­ence of cli­mat­ic con­di­tions and geo­log­i­cal changes, thick salt stra­ta were formed. The main mech­a­nism of pre­cip­i­ta­tion is relat­ed to evap­o­ra­tion, when the con­cen­tra­tion of dis­solved salts in water increas­es and they begin to crys­tal­lize. Ini­tial­ly, less sol­u­ble sub­stances (car­bon­ates and sul­fates) pre­cip­i­tate, and with a fur­ther increase in con­cen­tra­tion, sodi­um chlo­ride pre­cip­i­tates. In deep­er lay­ers, pres­sure and tem­per­a­ture changes can con­tribute to the com­paction of salt deposits, form­ing mono­lith­ic deposits.

Tec­ton­ic process­es also play a sig­nif­i­cant role in the for­ma­tion of salt deposits. Salts have high plas­tic­i­ty, which allows them to move with­in the Earth­’s inte­ri­or, form­ing so-called salt domes or stocks. Such geo­log­i­cal struc­tures are known in many regions of the world, includ­ing Ukraine, where sig­nif­i­cant deposits of rock salt are con­cen­trat­ed in the Donet­sk, Dnipro-Donet­sk, Zakarpat­tia, and oth­er basins.

Distribution in Ukraine

The Donet­sk salt basin is one of the old­est and most impor­tant in Ukraine. It is locat­ed with­in the Bakhmut basin, and the salt lay­ers lie at depths of 100 to 1,500 meters. The thick­ness of these deposits varies from 100 to 360 meters. The salt deposits here were formed in the Meso­zoic era and are among the rich­est in the coun­try. Among the main deposits, it is worth high­light­ing Artemivsk, Slo­vian­sk, and Novokarfa­genske.

The Artemivske deposit is the largest in the basin, with reserves esti­mat­ed at 13.7 bil­lion tons. Salt is mined here using the under­ground min­ing method, and its qual­i­ty allows it to be used not only for tech­ni­cal pur­pos­es but also in the food indus­try.

The Slovyanske deposit has 890 mil­lion tons of reserves and is devel­oped using under­ground brine extrac­tion, which allows for the pro­duc­tion of a high­ly con­cen­trat­ed salt solu­tion.

The Novokarpha­genske deposit con­tains 478 mil­lion tons of salt and is exploit­ed in a sim­i­lar way.

The Dnipro-Donets Basin is less well known but also has sig­nif­i­cant salt reserves. Salt deposits were first dis­cov­ered here in 1932 near the city of Rom­ny. The salt dome struc­tures of this basin were formed dur­ing the Devon­ian peri­od, which ensured their con­sid­er­able thick­ness. The main deposits are Rom­ny and Yefremivske.

The Rom­ny deposit, locat­ed 7–9 km from the city of Rom­ny, con­tains 435.9 mil­lion tons of salt. Its unique­ness lies in the fact that it con­tains so-called mega­liths — com­pact salt for­ma­tions that can be extreme­ly thick. There were plans to build a soda plant based on this deposit, but the project was nev­er imple­ment­ed due to a lack of the nec­es­sary raw mate­ri­als.

The Yefremivske deposit, locat­ed in the Kharkiv region, has 539.7 mil­lion tons of salt reserves. The brine extrac­tion method is used here, and the Khim­prom enter­prise extracts up to 270,000 tons of salt annu­al­ly.

The Tran­scarpathi­an salt basin is unique in that the salt deposits here are strat­i­form and lie at depths of over 1,500 meters. Among the most impor­tant deposits are Solotvyno and Tere­bovlia.

The Solotvyno deposit is the most active­ly devel­oped in Tran­scarpathia. Its reserves are esti­mat­ed at 457 mil­lion tons. The deposits are rod-shaped, and extrac­tion is car­ried out by min­ing. Salt from this deposit is active­ly export­ed to Euro­pean coun­tries, in par­tic­u­lar to the Czech Repub­lic, Hun­gary, Moldo­va, and the Baltic states.

The Tere­bovlya deposit con­tains 1.396 bil­lion tons of salt, but is not cur­rent­ly being devel­oped.

The Pre­carpathi­an salt basin is an impor­tant cen­ter for the extrac­tion of potas­si­um and mag­ne­sium salts, which are used in the pro­duc­tion of min­er­al fer­til­iz­ers. Salt deposits here are asso­ci­at­ed with Neo­gene rocks. The largest deposit is Steb­nyk, which pro­vides raw mate­ri­als for the Polim­in­er­al com­pa­ny.

The Steb­nyk deposit con­tains 250 mil­lion tons of salt, which lies in the form of dozens of lens­es and lay­ers of potas­si­um salts. It is being devel­oped using under­ground leach­ing.

Nat­ur­al brine deposits have also been explored in the region, includ­ing Bolekhiv, Doly­na, and Dro­hobych. The Doly­na salt plant has a design capac­i­ty of 15,000 tons of salt per year, and the Dro­hobych plant pro­duces about 11,000 tons of salt annu­al­ly.

In south­ern Ukraine, salt deposits are rep­re­sent­ed by self-pre­cip­i­tat­ing salt formed in nat­ur­al reser­voirs. The Syvash and Sasyk-Syvash deposits are of great impor­tance here.

The Syvash deposit cov­ers an area of over 2,500 km² and is notable for the fact that salt is extract­ed here nat­u­ral­ly – by evap­o­rat­ing water in basins. The process depends on the direc­tion of the wind, which can change the hydro­log­i­cal regime of the reser­voirs.

The Sasyk-Sivash deposit is also used for the extrac­tion of salt, which forms in the thick­ness of lake silt.

Uses of rock salt

Rock salt plays an extreme­ly impor­tant role in human life and in var­i­ous indus­tries. Its most well-known use is in the food indus­try. It not only gives food its famil­iar salty taste, but also per­forms an impor­tant phys­i­o­log­i­cal function—it helps reg­u­late the body’s water-salt bal­ance. Sodi­um chlo­ride is the main source of sodi­um ions, which are nec­es­sary for con­duct­ing nerve impuls­es, mus­cle con­trac­tion, and main­tain­ing the osmot­ic bal­ance of cells. With­out suf­fi­cient salt, the body can­not func­tion nor­mal­ly.

Since ancient times, salt has been used as a nat­ur­al preser­v­a­tive. Its anti­sep­tic prop­er­ties pre­vent the growth of bac­te­ria and fun­gi, allow­ing meat, fish, veg­eta­bles, and dairy prod­ucts to be stored for long peri­ods of time. Salt­ing and mar­i­nat­ing became the main meth­ods of pre­serv­ing food long before the advent of refrig­er­a­tors.

Rock salt also plays an impor­tant role in the chem­i­cal indus­try. It is a raw mate­r­i­al for the pro­duc­tion of such impor­tant sub­stances as hydrochlo­ric acid, soda, chlo­rine, and sodi­um. Many process­es in the phar­ma­ceu­ti­cal indus­try depend on it, where it is used to pre­pare saline solu­tion, which is used for dehy­dra­tion of the body, as well as a basis for some med­i­cines. In the tex­tile and leather indus­tries, salt is used for fab­ric pro­cess­ing and leather tan­ning, which allows mate­ri­als to be giv­en the nec­es­sary prop­er­ties and pre­vents their dete­ri­o­ra­tion.

In agri­cul­ture, salt is used to feed farm ani­mals, as it con­tributes to the prop­er func­tion­ing of their bod­ies. It is also used in feed prepa­ra­tion, in par­tic­u­lar for silage and hay salt­ing. Some pest con­trol meth­ods also involve the use of sodi­um chlo­ride.

In the con­struc­tion indus­try, salt is used as a com­po­nent in the pro­duc­tion of spe­cial build­ing mate­ri­als. Its abil­i­ty to low­er the freez­ing point of water has found appli­ca­tion in road main­te­nance: in win­ter, it is used to com­bat ice by spread­ing it on roads, which sig­nif­i­cant­ly improves road safe­ty.

Anoth­er impor­tant area is refrig­er­a­tion, where salt is used in the form of brines. These allow low tem­per­a­tures to be cre­at­ed with­out the need for com­plex tech­ni­cal equip­ment, mak­ing them indis­pens­able in some pro­duc­tion process­es. Rock salt is also used in water purifi­ca­tion sys­tems, where it helps to soft­en water by remov­ing excess cal­ci­um and mag­ne­sium ions.

Thus, rock salt is not only an impor­tant food addi­tive, but also a ver­sa­tile indus­tri­al resource used in a wide vari­ety of human activ­i­ties. From the chem­i­cal and phar­ma­ceu­ti­cal indus­tries to agri­cul­ture and road con­struc­tion, this nat­ur­al min­er­al con­tin­ues to be indis­pens­able in the mod­ern world.