Opo­ka. Prop­er­ties, uses and prospects

Opo­ka is a rock of organ­ic and inor­gan­ic ori­gin, com­posed pri­mar­i­ly of sil­i­ca (SiO₂), which forms a hard but porous mate­r­i­al. Like oth­er opal-cristo­balite rocks, opo­ka is used as a hydraulic addi­tive in the man­u­fac­ture of var­i­ous types of cement. Opo­ka is includ­ed in the list of min­er­als of nation­al impor­tance approved by the Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine dat­ed Decem­ber 12, 1994, No. 827, as sorp­tion raw mate­r­i­al, cement raw mate­r­i­al, and raw mate­r­i­al for sawn wall mate­ri­als.

Origin and Properties

Opo­ka is one of the vari­eties of sed­i­men­ta­ry siliceous rocks, and its for­ma­tion occurs as a result of the accu­mu­la­tion of siliceous mate­r­i­al from micro­scop­ic organ­isms such as diatoms or sponges. Opo­ka belongs to the group of opal-cristo­balite rocks of sed­i­men­ta­ry and vol­canic-sed­i­men­ta­ry ori­gin, along with diatomites, radi­o­lar­ites, spon­go­lites, and tre­pels. Unlike diatomites, spon­go­lites, and tre­pel, opo­ka is dense­ly cement­ed but has high poros­i­ty.

Opo­ka has low den­si­ty and rel­a­tive­ly high poros­i­ty, mak­ing it lighter than oth­er siliceous rocks such as quartzite or flint. The col­or of opo­ka can vary from light gray to yel­low­ish or even brown, depend­ing on impu­ri­ties.

The main prop­er­ties of opal-cristo­balite rocks are:

• abil­i­ty to absorb col­loidal sub­stances from solu­tions and retain mechan­i­cal impu­ri­ties dur­ing liq­uid fil­tra­tion;
• high poros­i­ty and sig­nif­i­cant heat resis­tance;
• rel­a­tive­ly low hard­ness and abil­i­ty to eas­i­ly crum­ble into fine pow­der;
• chem­i­cal resis­tance to acids and alka­lis.

The main chem­i­cal com­po­nent of opo­ka is sil­i­con diox­ide (sil­i­ca), which con­sti­tutes about 90–95% of its com­po­si­tion. It also con­tains small impu­ri­ties of iron oxides, clay mate­ri­als, and organ­ic remains.

Areas of use

Opo­ka is not just a nat­ur­al raw mate­r­i­al, but a mate­r­i­al with broad prospects that has sig­nif­i­cant poten­tial in var­i­ous tech­no­log­i­cal process­es and spheres of life.

In the con­struc­tion indus­try, it is used as a com­po­nent for cement pro­duc­tion, which helps improve the mechan­i­cal prop­er­ties of build­ing mate­ri­als. Due to its high poros­i­ty, opo­ka is wide­ly used in water treat­ment and fil­tra­tion sys­tems, pro­vid­ing effec­tive purifi­ca­tion of water and oth­er liq­uids.

The met­al­lur­gi­cal indus­try also uses opo­ka for the pro­duc­tion of refrac­to­ry mate­ri­als need­ed for high-tem­per­a­ture process­es. In the chem­i­cal indus­try, it is used for the sorp­tion of harm­ful sub­stances and waste treat­ment.

In envi­ron­men­tal pro­grams, opo­ka helps solve prob­lems of pro­cess­ing and reduc­ing envi­ron­men­tal pol­lu­tion. This makes it indis­pens­able for enter­pris­es striv­ing for envi­ron­men­tal­ly clean pro­duc­tion. The use of opo­ka also finds its place in agri­cul­ture, par­tic­u­lar­ly as a com­po­nent of fer­til­iz­ers or for improv­ing soil con­di­tions, as it helps retain mois­ture and nutri­ents.

Addi­tion­al­ly, opo­ka can be used as a basis for cre­at­ing var­i­ous com­pos­ite mate­ri­als, which extends its appli­ca­tion in inno­v­a­tive tech­nolo­gies and sci­en­tif­ic devel­op­ments, par­tic­u­lar­ly in envi­ron­men­tal and con­struc­tion projects.

Deposits in Ukraine

In Ukraine, opo­ka is found in sev­er­al regions, and its deposits have impor­tant eco­nom­ic and indus­tri­al sig­nif­i­cance. The State Bal­ance of Ukraine accounts for 7 opo­ka deposits in Don­bas, DDB (Dnipro-Donets Basin), Azov region, Black Sea and Lviv basins, and Crimea, with bal­ance reserves of 67,280 thou­sand tons and off-bal­ance reserves of 3,246 thou­sand tons.

The Bal­ka Mokra deposit is locat­ed in the Amvrosi­iv­ka dis­trict of Donet­sk region and is rep­re­sent­ed by an opo­ka deposit asso­ci­at­ed with Upper Cre­ta­ceous sed­i­ments. Its length is about 2 km, and its width varies from 2 to 380 m. The thick­ness also varies, being 0.5 m on the wings of the trough and reach­ing 70 m in its cen­tral part. The total reserves of the min­er­al with these deposit para­me­ters are esti­mat­ed at 20.5 mil­lion tons. The deposit was devel­oped by JSC “Don­ce­ment.”

The Rava-Rus­ka deposit is locat­ed near the epony­mous dis­trict cen­ter of Lviv region, rep­re­sent­ed by spon­go­lites and recrys­tal­lized lime­stones of the Cre­ta­ceous sys­tem. It is the raw mate­r­i­al base for the Myko­laiv cement plant, whose pro­duc­tion (about 2 mil­lion tons) is rep­re­sent­ed by Port­land cement for var­i­ous pur­pos­es.

The Mykhailivske and Pokrovske deposits are locat­ed in the Myko­laiv region. Indus­tri­al deposits are rep­re­sent­ed by lime­stones and opo­ka of the Kyiv suite of the Mid­dle Eocene and have a thick­ness of 8–11 meters. They are used as sawn wall stone and hydraulic addi­tive in cement pro­duc­tion. Cur­rent­ly, these deposits are not being devel­oped.

The Ter­nivs­ka sec­tion in the Novomyrhorod dis­trict of Kirovohrad region is being devel­oped under eco­nom­ic risk con­di­tions by LLC “SILI­KA”. The min­er­al is rep­re­sent­ed by opo­ka and opo­ka-like sand­stones of the Buchak series and Kyiv suite, with a thick­ness of up to 7.5m.

Addi­tion­al­ly, the Vodi­anske and Hostro­mo­hylske deposits in Luhan­sk region and the Nemi­iske deposit in Vin­nyt­sia region have been pre­lim­i­nar­i­ly eval­u­at­ed.

Ukrain­ian opo­ka deposits are main­ly used for cement pro­duc­tion, refrac­to­ry mate­ri­als, and con­struc­tion. How­ev­er, there is poten­tial for wider use of opo­ka in the chem­i­cal indus­try, fil­tra­tion sys­tems, and even in agri­cul­ture as a soil adsor­bent. Ukraine has sig­nif­i­cant poten­tial for fur­ther devel­op­ment of these deposits, but it is impor­tant to imple­ment mod­ern extrac­tion and pro­cess­ing tech­nolo­gies to reduce envi­ron­men­tal impact and increase the eco­nom­ic effi­cien­cy of using this min­er­al.

Opo­ka is a ver­sa­tile min­er­al with unique phys­i­cal and chem­i­cal prop­er­ties that make it impor­tant for many indus­tries. Its nat­ur­al resources require ratio­nal use and pro­tec­tion, which will allow pre­serv­ing this valu­able rock for future gen­er­a­tions. The study of new deposits and expan­sion of pro­duc­tion can con­tribute to increas­ing the eco­nom­ic ben­e­fits from opo­ka extrac­tion, espe­cial­ly in con­di­tions of grow­ing demand for con­struc­tion mate­ri­als both in Ukraine and abroad.