Ura­ni­um is a radioac­tive ele­ment of the actinide group with atom­ic num­ber 92, which in nature is pre­dom­i­nant­ly rep­re­sent­ed by the iso­tope ^238U with a half-life of about 4.5 bil­lion years. It is a heavy sil­very-white met­al with a den­si­ty exceed­ing 19 g/cm³, exhibit­ing sev­er­al oxi­da­tion states, the most sta­ble of which are +4 and +6. Its aver­age con­tent in the Earth’s crust is about 2.5×10⁻⁴%, with ele­vat­ed con­cen­tra­tions in acidic igneous rocks and car­bona­ceous shales. Under nat­ur­al con­di­tions, ura­ni­um migrates main­ly in oxi­diz­ing envi­ron­ments in the form of uranyl ions and com­plex­es, pre­cip­i­tat­ing in reduc­ing zones, which leads to the for­ma­tion of ore deposits.

Ura­ni­um ores 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 ores of radioac­tive met­als.

Physicochemical properties

Ura­ni­um (U) is a radioac­tive actinide with atom­ic num­ber 92 and atom­ic mass 238.0289. In nature, the iso­tope ^238U pre­dom­i­nates, with a half-life of about 4.5×10⁹ years. It is a sil­very-white met­al with a den­si­ty of approx­i­mate­ly 19 g/cm³, melt­ing at about 1130 °C and boil­ing at 3500 °C. Ura­ni­um is chem­i­cal­ly reac­tive and exhibits oxi­da­tion states from +2 to +6, the most sta­ble being +4 and +6. Its main nat­ur­al oxide is U₃O₈. Ura­ni­um read­i­ly dis­solves in nitric and hydrochlo­ric acids and forms numer­ous alloys with met­als. Its aver­age con­tent in the Earth’s crust is 2.5×10⁻⁴%, with the high­est con­cen­tra­tions asso­ci­at­ed with acidic igneous rocks and car­bona­ceous shales. A key prop­er­ty of ura­ni­um is its spon­ta­neous decay into radi­ogenic lead, which is used for deter­min­ing the absolute age of rocks. The half-lives of ^235U and ^234U are 8.91×10⁸ and 2.235×10⁵ years, respec­tive­ly.

When exceed­ing a crit­i­cal mass, ura­ni­um can sus­tain a nuclear chain reac­tion, which under uncon­trolled con­di­tions leads to an explo­sion, while in con­trolled con­di­tions it enables reg­u­lat­ed “burn­ing” in reac­tors. In nature, ura­ni­um migrates main­ly in oxi­diz­ing alka­line and neu­tral envi­ron­ments as uranyl ions and com­plex­es, pre­cip­i­tat­ing under reduc­ing con­di­tions. Redox bar­ri­ers are key zones of ura­ni­um accu­mu­la­tion.

Ura­ni­um ores include more than a hun­dred known min­er­als: oxides (urani­nite, pitch­blende), hydrox­ides, sil­i­cates (coffi­nite, ura­no­phane, kaso­lite), car­bon­ates, sul­fates, phos­phates, vana­dates, molyb­dates, titanates, and mixed Ta–Nb–Ti phas­es. It also com­mon­ly occurs as an iso­mor­phic impu­ri­ty in zir­con, mon­azite, xeno­time, leu­cox­ene, and iron and man­ganese hydrox­ides.

Use and raw material requirements

Dis­cov­ered by M. Klaproth in 1789, ura­ni­um ini­tial­ly had lim­it­ed appli­ca­tions, but after the dis­cov­ery of radioac­tiv­i­ty and radi­um in the late 19th cen­tu­ry, it became wide­ly stud­ied, and since the 1940s — indus­tri­al­ly mined. Today, it is main­ly used as fuel for nuclear reac­tors, includ­ing marine reac­tors, as well as for radi­a­tion shield­ing, spe­cial glass and ceram­ics, and cer­tain alloys.

The eco­nom­ic val­ue of ura­ni­um ores depends on their grade and tech­no­log­i­cal prop­er­ties. High-grade ores con­tain more than 1% U, while low-grade ores con­tain less than 0.05%. Ore mate­r­i­al may be sil­i­cate, car­bon­ate, sul­fide, iron-oxide, phos­phate, or organ­ic in nature. Ore tex­tures range from coarse-grained to col­loidal-dis­persed. Unwant­ed impu­ri­ties such as cal­ci­um and mag­ne­sium car­bon­ates, apatite, sul­fates, humic sub­stances, and sul­fides com­pli­cate pro­cess­ing.

Pro­cess­ing of ura­ni­um ores includes mechan­i­cal ben­e­fi­ci­a­tion (radio­met­ric sort­ing, grav­i­ty sep­a­ra­tion, flota­tion), acid or car­bon­ate leach­ing, and in-situ leach­ing for infil­tra­tion-type ores. Tech­nolo­gies for ura­ni­um extrac­tion from sea­wa­ter are also being inves­ti­gat­ed. Along­side ura­ni­um, by-prod­ucts such as vana­di­um, phos­pho­rus, molyb­de­num, rare earth ele­ments, tan­ta­lum, nio­bi­um, and scan­di­um may be recov­ered.

Genetic types of deposits and global distribution

Ura­ni­um ores form under endoge­nous (mag­mat­ic, peg­matitic, hydrother­mal, meta­so­mat­ic, and meta­mor­phic), exoge­nous (sed­i­men­ta­ry, vol­canogenic-sed­i­men­ta­ry, and infil­tra­tion), and poly­genic con­di­tions. The most impor­tant deposit types include uncon­for­mi­ty-type deposits (Cana­da, Aus­tralia), sand­stone-type deposits (USA, Kaza­khstan, Uzbek­istan, Niger), vein-type deposits (Rus­sia, Cana­da), gran­ite-relat­ed deposits (Namib­ia), brec­cia-type deposits asso­ci­at­ed with copper–gold–silver min­er­al­iza­tion (Aus­tralia), con­glom­er­ate-type deposits (South Africa), and meta­so­mat­ic deposits (includ­ing those in Ukraine).

Sand­stone-type deposits are con­fined to plat­form sand­stones and are enriched at the bound­ary between oxi­da­tion zones and reduc­ing con­di­tions. Uncon­for­mi­ty-type deposits form at the con­tact between the Pre­cam­bri­an base­ment and the plat­form cov­er and are char­ac­ter­ized by very high ura­ni­um grades.

Uranium ore deposits in Ukraine

In Ukraine, nuclear pow­er plants account for about 40–45% of elec­tric­i­ty pro­duc­tion; there­fore, a domes­tic ura­ni­um resource base is of strate­gic impor­tance. Esti­mat­ed resources amount to 366 thou­sand tons of U, with explored reserves of 31 thou­sand tons. About 21 deposits are known, and annu­al pro­duc­tion is approx­i­mate­ly 500 tons of U.

In Ukraine, ura­ni­um ores are rep­re­sent­ed by sev­er­al main genet­ic types that dif­fer in for­ma­tion con­di­tions, min­er­al­o­gy, and indus­tri­al char­ac­ter­is­tics. In the Kirovohrad region, meta­so­mat­ic and hydrother­mal-meta­so­mat­ic deposits are asso­ci­at­ed with albitites and alka­line meta­so­matites, includ­ing the Sev­erynivske, Vatutinske, Michurinske, and Kom­paniyivske deposits. The Sev­erynivske deposit is char­ac­ter­ized by large albitite bod­ies over 1 km long and up to 1 km deep, enriched in urani­nite, bran­ner­ite, coffi­nite, and sec­ondary ura­ni­um sil­i­cates; it is cur­rent­ly in reserve. The Vatutinske deposit includes three main ore bod­ies with­in a 3 km-long albitite zone, con­tain­ing urani­nite, nas­tu­ran, “ura­ni­um black,” coffi­nite, ura­no­phane, beta-ura­n­otile, bran­ner­ite, and davidite; iso­topic dat­ing indi­cates an ore for­ma­tion age of about 1.8 bil­lion years. The Michurinske deposit is asso­ci­at­ed with the Main Fault zone and con­tains fine­ly dis­sem­i­nat­ed and vein-type ores with ura­no­phane, ura­ni­um black, and ura­ni­um sil­i­cates, local­ly with high-grade Bi–U min­er­al­iza­tion.

Meta­mor­phogenic (iron-ura­ni­um) deposits include those of the Kryvyi Rih–Kremenchuk zone in the Dnipropetro­vsk region, par­tic­u­lar­ly the Zhov­torichenske deposit, where ura­ni­um min­er­al­iza­tion is asso­ci­at­ed with alka­line meta­so­matites (albitites, aegirinites, riebeckite–carbonate vari­eties) and iron-car­bon­ate meta­so­matites. Ore types include urani­nite, bran­ner­ite, nenad­ke­vite, coffinite–nasturan–brannerite, sulfide–nasturan, and malacon–apatite ores. Asso­ci­at­ed ele­ments include scan­di­um, vana­di­um, tita­ni­um, zir­co­ni­um, hafni­um, and rare earth ele­ments.

Peg­matitic and vein-type deposits such as Yuzhne, Lozo­vatske, and Kalynivske are relat­ed to peg­matites and aplite-peg­matites and con­tain urani­nite, ura­ni­um black, zir­cono­lite, and mon­azite. The Myko­lo-Kozelske con­glom­er­ate-type deposit is an Osado­vo-meta­mor­phosed deposit where ura­ni­um (as nas­tu­ran) is con­cen­trat­ed in the cement of con­glom­er­ates togeth­er with pyrite, and also con­tains mon­azite, zir­con, and sul­fides.

Ura­ni­um-bitu­men deposits asso­ci­at­ed with salt domes include Adamivske, Kras­nooskolske, and Berekke deposits, where sol­id bitu­mens (oxy-anthrax­o­lites, oxykerites) are enriched in ura­ni­um up to 1–2%. Asso­ci­at­ed ele­ments include vana­di­um, molyb­de­num, mer­cury, lead, zinc, and gold. Infil­tra­tion-type deposits of the Dnipro ura­ni­um dis­trict are asso­ci­at­ed with Eocene coal-bear­ing stra­ta and occur as lay­ered or lens-shaped mul­ti­level ore bod­ies. Ura­ni­um is main­ly con­cen­trat­ed in car­bona­ceous and clay mate­r­i­al, with aver­age grades of 0.015–0.03%, mak­ing them suit­able for in-situ leach­ing.

Thus, ura­ni­um ores are a strate­gic raw mate­r­i­al with­out which the func­tion­ing of mod­ern nuclear ener­gy and a num­ber of high-tech indus­tries would not be pos­si­ble. Their val­ue is deter­mined by ura­ni­um con­tent, min­er­alog­i­cal com­po­si­tion, and tech­no­log­i­cal prop­er­ties that influ­ence the choice of pro­cess­ing meth­ods. Ore deposits form under a wide range of geo­log­i­cal con­di­tions — from mag­mat­ic and hydrother­mal to sed­i­men­ta­ry and infil­tra­tion envi­ron­ments — with redox bar­ri­ers play­ing a key role in pre­cip­i­tat­ing ura­ni­um from solu­tion.

Ukraine has a sig­nif­i­cant resource base of ura­ni­um ores of var­i­ous genet­ic types; how­ev­er, indus­tri­al devel­op­ment is com­pli­cat­ed by the rel­a­tive­ly low aver­age met­al con­tent and the pre­dom­i­nance of under­ground min­ing, which increas­es pro­duc­tion costs. Improv­ing effi­cien­cy is pos­si­ble through the intro­duc­tion of more eco­nom­i­cal tech­nolo­gies, the devel­op­ment of in-situ leach­ing meth­ods, and the explo­ration of new promis­ing deposits.