High-alu­mi­na raw mate­ri­als, rep­re­sent­ed by min­er­als such as sil­i­man­ite (Al₂­SiO₅), kyan­ite (dis­tene) (Al₂­SiO₅) and andalusite (Al₂­SiO₅), are poly­mor­phic mod­i­fi­ca­tions of the same chem­i­cal com­po­si­tion – alu­mi­nosil­i­cate. Due to their unique phys­i­cal and chem­i­cal prop­er­ties, these min­er­als are wide­ly used in the pro­duc­tion of high-qual­i­ty refrac­to­ries, alka­li-acid-resis­tant mate­ri­als, met­al ceram­ics and oth­er engi­neer­ing fields.

Sil­i­man­ite and kyan­ite are includ­ed in the list of min­er­als of nation­al impor­tance approved by Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine No. 827 of 12 Decem­ber 1994, as raw mate­ri­als for refrac­to­ries.

Chemical properties

Min­er­als of the sil­i­man­ite group are char­ac­terised by the same chem­i­cal com­po­si­tion (Al₂­SiO₅), but dif­fer­ent crys­tal struc­tures, which deter­mine their phys­i­cal prop­er­ties. The main ele­ment is alu­mini­um (Al), which pro­vides high refrac­tori­ness and resis­tance to aggres­sive chem­i­cal envi­ron­ments. Typ­i­cal impu­ri­ties: Fe₂O₃, TiO₂, MgO, K₂O, Na₂O.

Physical properties

• Sil­i­man­ite: has a nee­dle-like or pris­mat­ic crys­tal struc­ture, hard­ness on the Mohs scale – 6.5–7.0, den­si­ty – 3.23–3.24 g/cm³, melt­ing point – about 1,540 °C.
• Kyan­ite: forms thin pris­mat­ic crys­tals or grains, hard­ness – 4.5–5.0 in the direc­tion of cleav­age and 6.5–7.0 in the per­pen­dic­u­lar direc­tion, den­si­ty – 3.53–3.65 g/cm³, melt­ing point – 1,650 °C.
• Andalusite: often found in the form of short pris­mat­ic crys­tals, hard­ness – 6.5–7.5, den­si­ty – 3.1–3.2 g/cm³, melt­ing point – about 1,400 °C.

These min­er­als demon­strate high ther­mal sta­bil­i­ty, low ther­mal expan­sion coef­fi­cient and good resis­tance to mechan­i­cal and chem­i­cal stress­es, which makes them indis­pens­able in the pro­duc­tion of refrac­to­ries and met­al ceram­ics.

Genesis of sillimanite, kyanite and andalusite

Sil­i­man­ite, kyan­ite and andalusite are formed main­ly in meta­mor­phic rocks under the influ­ence of high tem­per­a­tures and pres­sures. Geo­log­i­cal con­di­tions favour the for­ma­tion of these min­er­als in meta­mor­phic schists, gneiss­es, quartzites, as well as in con­tact-meta­mor­phic zones near gran­ite intru­sions. Their for­ma­tion is due to the trans­for­ma­tion of clayey or alu­mini­um-rich rocks in zones of medi­um and high-grade meta­mor­phism.

• Sil­i­man­ite – formed at high tem­per­a­tures and medi­um pres­sures.
• Kyan­ite – formed at high pres­sures and rel­a­tive­ly low tem­per­a­tures.
• Andalusite – crys­tallis­es at low pres­sures and mod­er­ate tem­per­a­tures.

Distribution in Ukraine

The main occur­rences of this raw mate­r­i­al in Ukraine are asso­ci­at­ed with Pre­cam­bri­an meta­mor­phic rocks of shales and gneiss­es in var­i­ous geo­log­i­cal zones, such as Pobuzhzhya, Pri­a­zovia, Kryvyi Rih-Kre­menchuk zone, as well as the Ovruch series of the Volyn block.

Accord­ing to the State Bal­ance, reserves of kyan­ite and sil­li­man­ite are con­cen­trat­ed in com­plex plac­er deposits, such as Maly­shevske (in oper­a­tion) and Vovchanske, as well as in two man-made deposits: Bal­ka Kru­ta (Dnipropetro­vsk region) and Tara­sivske (Kyiv region). The total proven reserves of these min­er­als in cat­e­gories A+B+C₁ amount to 2,037.7 thou­sand tonnes. In 2019, the pro­duc­tion of dis­tene-sil­i­man­ite con­cen­trate amount­ed to 89.8 thou­sand tonnes.

In the Azov region, promis­ing deposits include andalusite at the Huli­aipole iron ore deposit and sil­i­man­ite at the Dra­gun­sk corun­dum-sil­i­man­ite deposit, as well as at the Pavlivsk, Ser­hi­ivsk, Novoukrain­sk, Kor­sak, Kuk­sun­gur and Mar­i­upol iron ore deposits. The Dra­gun­skoye deposit has a pro­duc­tive hori­zon 150–300 m thick and 15 km long. There are lay­ers, stra­ta and lens­es (0.2–15 m) of sil­i­man­ite gneiss­es and schists, often with corun­dum, spinel, biotite and oth­er min­er­als. The sil­i­man­ite con­tent in the rocks varies from 1% to 45%, with an aver­age of 10–14%. The esti­mat­ed resources to a depth of 200 m are 61,000 tonnes of sil­i­man­ite with an aver­age con­tent of 10–12% and 728,000 tonnes of corun­dum with a con­tent of 1%.

In the Kirovo­grad region, the Kap­i­tanivsky and Solomiyivsky deposits are promis­ing. Kap­i­tanivskyi is char­ac­terised by thick gar­net-sil­i­man­ite-cordierite gneiss­es and schists (thick­ness 150–200 m, length up to 1.5 km), with a sil­i­man­ite con­tent in the rocks of 1.2–4.4%. The Solomiyivskyi deposit con­tains lay­ers of sil­i­man­ite-bear­ing rocks with a thick­ness of 1–13 m and a length of up to 1 km, with a sil­i­man­ite con­tent of 4.7–34.7%.

In Zhy­to­myr region , clay-rich raw mate­ri­als are found with­in the Perzhan­sk deposit, which is asso­ci­at­ed with Pale­o­pro­tero­zoic dis­tene quartzites and con­tains steep strat­i­form deposits up to 1,700 m long and 35–40 m thick. The aver­age dis­tene con­tent is 19.5%. The esti­mat­ed resources are 26.9 mil­lion tonnes. The Poby­chan­sky deposit, locat­ed in this area, has sim­i­lar char­ac­ter­is­tics, with esti­mat­ed resources of 66 mil­lion tonnes of dis­tene ore.

Plac­er con­cen­tra­tions of sil­li­man­ite and dis­thene have been found in such deposits as Maly­shevske, Vovchanske, Zeleno­yarske, Tara­sivske, Sel­ishchanske and Pravoberezhne. The ore fields are locat­ed in the Polta­va and Sar­ma­t­ian stra­ta with­in the Zhy­to­myr and Dnipropetro­vsk regions. The main min­er­als of these plac­ers are ilmenite, rutile, zir­con, sil­li­man­ite, dis­thene, gar­net, stau­ro­lite, andalusite, tour­ma­line, corun­dum, etc. The aver­age con­tent of sil­li­man­ite and dis­thene in the heavy frac­tion of sand is 13–74%, depend­ing on the loca­tion.

Deposits and ore occurrences of high-alumina raw materials

The Dra­gunske deposit is locat­ed with­in the Tem­ryuk region. The pro­duc­tive hori­zon, 150–300 m thick (220 m on aver­age) and 15 km long, is rep­re­sent­ed by packs, lay­ers, inter­lay­ers and lens­es of sil­i­man­ite, sil­i­man­ite-biotite, sil­i­man­ite-gar­net biotite, sil­i­man­ite-cordierite-biotite and spinel-sil­i­man­ite-biotite rocks con­tain­ing corun­dum, as well as gneiss­es and schists among deposits of migmatites and por­phyrit­ic gran­ites. The sil­i­man­ite con­tent varies from 1 to 45% and aver­ages 10–14%. It forms aci­c­u­lar and pris­mat­ic crys­tals, grains, sheaf-like, radi­at­ing and entan­gled fibrous aggre­gates, as well as inclu­sions in feldspars and thin inter­growths with biotite. The length of indi­vid­ual crys­tals reach­es 15 mm. The corun­dum con­tent ranges from 6 to 16%, aver­ag­ing 1–5%. High-alu­mi­na rocks con­tain 25–30%, some­times up to 38% Al₂O₃. The esti­mat­ed resources to a depth of 200 m in the P3 cat­e­go­ry are esti­mat­ed at 61 thou­sand tonnes of sil­li­man­ite (with an aver­age con­tent of 10–12%), 728 thou­sand tonnes of corun­dum (P2, with an aver­age con­tent of 1%) and over 2 mil­lion tonnes of asso­ci­at­ed abra­sive gar­net.

The Maly­shevske deposit pro­duces 20–30 thou­sand tonnes of dis­tene-sil­i­man­ite con­cen­trate annu­al­ly, which meets inter­na­tion­al stan­dards for chem­i­cal com­po­si­tion: Al₂O₃ – 57%, TiO₂ – 1.5%, Fe₂O₃ – 0.8%. Verkhned­niprovsky Min­ing and Met­al­lur­gi­cal Plant extracts con­cen­trates of ilmenite, rutile, zir­con, sil­i­man­ite, dis­tene and oth­er min­er­als from plac­ers.

The Smirnovske deposit has char­ac­ter­is­tics sim­i­lar to the Dra­gunske deposit, but it lacks corun­dum rocks. The esti­mat­ed resources of sil­li­man­ite in the P₃ cat­e­go­ry to a depth of 200 m are esti­mat­ed at 16 mil­lion tonnes with an aver­age con­tent of 20%.

At the Mar­i­upol deposit, lay­ers up to 28 m thick have been dis­cov­ered, con­tain­ing seams 2–12.5 m thick. The rocks are rep­re­sent­ed by sil­i­man­ite-gar­net-biotite, corun­dum-spinel-sil­i­man­ite-gar­net, corun­dum-biotite-sil­i­man­ite and corun­dum-sil­i­man­ite-spinel gneiss­es and schists. The sil­i­man­ite con­tent reach­es 35%, corun­dum – up to 10%. The pro­ject­ed resources of sil­i­man­ite (P3) to a depth of 200 m are 34.1 thou­sand tonnes, corun­dum – 1.6 thou­sand tonnes.

The Kap­i­tanivskyi occur­rence is rep­re­sent­ed by a thick­ness of gar­net-sil­i­man­ite-cordierite and gar­net-sil­i­man­ite gneiss­es and schists 150–200 m thick and up to 1.5 km long. The sil­i­man­ite con­tent in the rocks is 1.2–4.4%.

The Solomievske deposit is char­ac­terised by the pres­ence of sil­i­man­ite-bear­ing gneiss­es and schists, form­ing lay­ers 1–13 m thick and up to 1 km long, with a sil­i­man­ite con­tent of 4.7–34.7%.

The Perzhan­sk deposit is asso­ci­at­ed with dis­tene quartzites of the Palaeo-Pro­tero­zoic age. The ore bod­ies are steeply dip­ping strat­i­form deposits extend­ing up to 1,700 m with a thick­ness of 35–40 m, with sep­a­rate lens­es up to 15 m. The aver­age con­tent of dis­tene is 19.5%, mica – 10%, andalusite – 1%, and the total con­tent of hematite, ilmenite and mag­netite – 4%. The aver­age chem­i­cal com­po­si­tion of dis­tene quartzites is: SiO₂ – 70.8%, TiO₂ – 0.52%, Al₂O₃ – 20.8%, Fe₂O₃ – 0.71%, MnO – 0.02%, MgO – 0.11%, CaO – 0.58%, K₂O – 0.08%, Na₂O – 0.26%, P₂O₅ – 0.05%. The reserves of dis­tene ores to a depth of 87.5 m in cat­e­go­ry C2 are esti­mat­ed at 9.5 mil­lion tonnes, off-bal­ance reserves – 21.9 mil­lion tonnes, and pro­ject­ed resources – 26.9 mil­lion tonnes (Gursky et al., 2006). Dur­ing ore enrich­ment, the yield of dis­tene con­cen­trate is 8–90.5%.

The Poby­chan­sky deposit is sim­i­lar in its char­ac­ter­is­tics to the Perzhan­sky deposit, and the pro­ject­ed resources of dis­tene ore here reach 66 mil­lion tonnes.

Application of high-alumina raw materials

High-alu­mi­na raw mate­ri­als, rep­re­sent­ed by sil­li­man­ite, dis­thene and andalusite, have a wide range of uses due to their unique phys­i­cal and chem­i­cal prop­er­ties. One of the main areas of appli­ca­tion is the pro­duc­tion of refrac­to­ries. These min­er­als serve as the basis for the man­u­fac­ture of mate­ri­als with a high Al₂O₃ con­tent, which demon­strate high ther­mal sta­bil­i­ty and resis­tance to chem­i­cal­ly aggres­sive envi­ron­ments. They are used for lin­ing met­al­lur­gi­cal, cement and glass fur­naces, as well as in the chem­i­cal indus­try for the cre­ation of alka­li-acid-resis­tant reac­tors.

Sil­i­man­ite and andalusite raw mate­ri­als play an impor­tant role in the ceram­ic indus­try, par­tic­u­lar­ly in the pro­duc­tion of high-tem­per­a­ture ceram­ics used for tech­ni­cal pur­pos­es such as insu­la­tors, noz­zles and oth­er parts oper­at­ing at high tem­per­a­tures. In the field of abra­sives, these min­er­als are used along­side gar­net and corun­dum to ensure the effec­tive grind­ing, pol­ish­ing and cut­ting of met­als and glass.

Met­al ceram­ics are also a sig­nif­i­cant area of use for this raw mate­r­i­al. Sil­i­man­ite-based com­pos­ites are used in the aero­space, auto­mo­tive and engi­neer­ing indus­tries due to their high ther­mal sta­bil­i­ty and strength. In addi­tion, dis­thene and andalusite are active­ly used in the chem­i­cal indus­try to cre­ate cat­alyt­ic mate­ri­als and fil­ter ele­ments.

In con­struc­tion, high-alu­mi­na raw mate­ri­als are used to man­u­fac­ture spe­cial cements and con­cretes that retain their prop­er­ties in high tem­per­a­tures and aggres­sive envi­ron­ments. These mate­ri­als are also impor­tant for the ener­gy sec­tor, where they are used for lin­ing ther­mal pow­er plants, in par­tic­u­lar boil­ers and fur­naces at pow­er sta­tions.

Thus, sil­li­man­ite, dis­thene and andalusite are indis­pens­able in many indus­tries. Their use ensures the cre­ation of high-qual­i­ty prod­ucts that are of strate­gic impor­tance both for the domes­tic mar­ket of Ukraine and for the devel­op­ment of the coun­try’s export poten­tial.