Zeo­lites: prop­er­ties, uses and prospects

Zeo­litesare alu­mi­nosil­i­cate min­er­als with a crys­talline struc­ture and char­ac­ter­is­tic adsorp­tion prop­er­ties. They are known for their porous struc­tures that can cap­ture and retain mol­e­cules of oth­er sub­stances. Zeo­lites are wide­ly used in var­i­ous indus­tries, such as indus­try, ecol­o­gy and med­i­cine. Zeo­lites are 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 agro­chem­i­cal raw mate­ri­als, adsorp­tion raw mate­ri­als and cement raw mate­ri­als.

Zeo­lites are a group of min­er­als that are hydrat­ed alu­mi­nosil­i­cates of alka­li and alka­line earth met­als (sodi­um, cal­ci­um, potas­si­um, bar­i­um). They have unique crys­tal struc­tures with porous sys­tems that allow them to adsorb water and gas mol­e­cules, as well as exchange ions. There are about 40 known nat­ur­al zeo­lites, and they are formed by vol­canic activ­i­ty or alter­ation of clays, silts, and sed­i­men­ta­ry rocks. Let’s look at some of the most com­mon nat­ur­al zeo­lites.

1. Clinop­tilo­lite (Na,Ca,K)2 3Al3(Al,Si)2 Si13O36 • 12H2O
Clinop­tilo­lite is the most com­mon nat­ur­al zeo­lite. It has high poros­i­ty and ion exchange capac­i­ty, so it is wide­ly used in water and gas purifi­ca­tion and in agri­cul­ture as an adsor­bent and fer­til­iz­er. It is used to puri­fy water from ammo­nia and heavy met­als, and as an addi­tive in ani­mal feed.

2. Mor­den­ite (Ca(Na2,K2)[AlSi5O12]4 • 6H2O
Mor­den­ite is char­ac­ter­ized by high ther­mal and chem­i­cal sta­bil­i­ty. Its porous struc­ture allows it to adsorb mol­e­cules with nar­row diam­e­ters, which makes it effec­tive in cat­alyt­ic reac­tions and gas purifi­ca­tion. It is used in the petro­chem­i­cal indus­try, as well as in air purifi­ca­tion fil­ters.

3. Natro­lite Na₂[Al₂Si₃O₁₀] • 2H₂O
Natro­lite is known for its high adsorp­tion and ion exchange capac­i­ty. It has a fibrous or colum­nar struc­ture and is often found in the voids of basalt rocks, as well as in hydrother­mal deposits. Due to its high hydrophilic­i­ty, natro­lite effec­tive­ly adsorbs water mol­e­cules and var­i­ous cations. Natro­lite is used for water purifi­ca­tion, removal of pol­lu­tants from soils, and as a raw mate­r­i­al in the pro­duc­tion of build­ing mate­ri­als. It is also used in the chem­i­cal indus­try for ion exchange process­es.

4. Chabazite (Ca,Na_2,K_2) 4[Al8Si40O96] • 24H2O
Chabazite has high adsorp­tion prop­er­ties and is often used as a mol­e­c­u­lar sieve. Its porous struc­ture allows it to effec­tive­ly retain water mol­e­cules and oth­er small mol­e­cules. It is used for air and water purifi­ca­tion, as well as in build­ing mate­ri­als for soil sta­bi­liza­tion.

5. Lam­on­tite Ca(Al2Si4O12) • 4H2O
Lam­on­tite is known for its ten­den­cy to dehy­drate at ele­vat­ed tem­per­a­tures, which leads to a par­tial loss of its crys­tal struc­ture. How­ev­er, it effec­tive­ly adsorbs water mol­e­cules in cold con­di­tions. It is main­ly used in con­struc­tion and as an adsor­bent in low-tem­per­a­ture process­es.

6. Stil­bite NaCa4[(Al9Si27)O72] • 28H2O
Stil­bite has a lamel­lar or fibrous struc­ture and exhibits high adsorp­tion prop­er­ties for water. Its crys­tals are often found in the voids of basalt rocks. It is used as an adsor­bent in water fil­ters, as well as in the con­struc­tion indus­try.

7. Phillip­site (K,Na,Ca)2(Si,Al)8O16 • 6H2O
Phillip­site has good ion exchange and adsorp­tion capac­i­ty for water and ammo­ni­um mol­e­cules. It is formed in basalt rocks and sed­i­ments. It is used for water and soil purifi­ca­tion, as well as in agri­cul­ture as a fer­til­iz­er.

8. Eri­on­ite (Na,K,Ca)2Al4Si14O36 • 15H2O
Eri­on­ite has a fibrous struc­ture and high adsorp­tion capac­i­ty, but it is also known to be poten­tial­ly haz­ardous to health due to car­cino­genic prop­er­ties (sim­i­lar to asbestos). Its use is lim­it­ed due to pos­si­ble health risks, but it was pre­vi­ous­ly used for water and gas purifi­ca­tion.

Properties of zeolites

Zeo­lites have unique physic­o­chem­i­cal prop­er­ties that make them use­ful in a vari­ety of indus­tri­al and sci­en­tif­ic appli­ca­tions. One of the main char­ac­ter­is­tics of zeo­lites is their high selec­tiv­i­ty for cer­tain mol­e­cules or ions, which makes them indis­pens­able in cat­alyt­ic crack­ing process­es, gas purifi­ca­tion, and in med­i­cine for detox­i­fi­ca­tion of the body.

Zeo­lites con­sist of sil­i­con and alu­minum tetra­he­dra con­nect­ed through oxy­gen atoms, form­ing a com­plex three-dimen­sion­al net­work of pores and chan­nels. This struc­ture allows zeo­lites to adsorb ions and mol­e­cules of water, gas­es, and oth­er sub­stances. They also have ion-exchange prop­er­ties, which makes them use­ful for water and gas purifi­ca­tion.

The main prop­er­ties of zeo­lites are as fol­lows:

• Poros­i­ty. The inter­nal struc­ture of zeo­lites con­tains large pores and chan­nels with a diam­e­ter of 3 to 10 angstroms. These pores make zeo­lites excel­lent adsor­bents, capa­ble of cap­tur­ing mol­e­cules of a cer­tain size.
• Ther­mal sta­bil­i­ty. Most zeo­lites can with­stand tem­per­a­tures up to 700–800 °C with­out chang­ing their struc­ture. This prop­er­ty makes them use­ful in high-tem­per­a­ture process­es such as catal­y­sis.
• Mechan­i­cal strength. Zeo­lites have good mechan­i­cal strength, which allows them to be used under con­di­tions of high pres­sure and intense mechan­i­cal stress. This is impor­tant in indus­tri­al process­es where hard­ness and abra­sion resis­tance are key.
• Hydrophilic­i­ty. Zeo­lites can be either hydrophilic or hydropho­bic, depend­ing on their chem­i­cal com­po­si­tion. Hydrophilic zeo­lites effec­tive­ly adsorb water, which is used, for exam­ple, to dry gas­es or liq­uids.
• Cat­alyt­ic activ­i­ty. Zeo­lites are excel­lent cat­a­lysts in many chem­i­cal reac­tions, espe­cial­ly those occur­ring on the sur­face of solids. Due to their struc­ture, zeo­lites can act as mol­e­c­u­lar sieves, allow­ing only mol­e­cules of a cer­tain size and shape to enter their pores. This is espe­cial­ly impor­tant in petro­chem­i­cal crack­ing process­es and the syn­the­sis of oth­er chem­i­cal com­pounds.
• Sta­bil­i­ty to acids and alka­lis. Zeo­lites are gen­er­al­ly resis­tant to the action of weak acids and alka­lis. How­ev­er, their chem­i­cal resis­tance can vary depend­ing on the specifics of the struc­ture and com­po­si­tion. Some syn­thet­ic zeo­lites demon­strate increased resis­tance to aggres­sive chem­i­cal envi­ron­ments.
• Adsorp­tion prop­er­ties. Zeo­lites can adsorb var­i­ous mol­e­cules, includ­ing gas­es and liq­uids. This adsorp­tion abil­i­ty is based on their inter­nal porous struc­ture. Zeo­lites can effec­tive­ly absorb mol­e­cules of water, ammo­nia, car­bon diox­ide and oth­er gas­es.

Zeo­lites have a unique abil­i­ty to absorb gas mol­e­cules after dehy­dra­tion, the size of which does not exceed the size of the “input win­dows” to the intracrys­talline cav­i­ties. This prop­er­ty makes zeo­lites effec­tive sor­bents. Due to the spe­cial crys­tal struc­ture, the cav­i­ties of the crys­tals and access to them through the win­dows are arranged as reg­u­lar­ly as the atoms in the crys­tal lat­tice, which turns zeo­lites into a mol­e­c­u­lar sieve. When mol­e­cules that do not meet the required para­me­ters in size and con­fig­u­ra­tion are passed through this sieve, they are fil­tered out.

Nat­ur­al zeo­lites exhib­it selec­tiv­i­ty in the adsorp­tion of gas­es such as CO2 and SO2, which allows them to be used for the purifi­ca­tion of exhaust gas­es in indus­tri­al process­es, as well as for air purifi­ca­tion in closed sys­tems. Despite the fact that syn­thet­ic zeo­lites demon­strate high effi­cien­cy in many process­es, their use is often accom­pa­nied by dif­fi­cul­ties, espe­cial­ly due to insta­bil­i­ty in high-tem­per­a­ture con­di­tions.

Zeolites in Ukraine

In Ukraine, the state bal­ance sheet records the reserves of three deposits in the Zakarpat­tia region. These are Sokyrnytske, Sary­hych (Sokyrnytske) and Zelenokamyane. The total reserves of these deposits exceed 125 mil­lion tons. Oth­er deposits have also been explored in Zakarpat­tia near the vil­lage of Lypcha in the Khust dis­trict and the vil­lage of Vodyt­sia in the Tyachiv dis­trict.

The Sokyrnytske deposit is unique due to its scale and high qual­i­ty of min­er­als. The pro­duc­tive zone con­sists of gen­tle deposits of the upper hori­zon of pla­gi­oli­parit­ic tuffs, where the clinop­tilo­lite con­tent increas­es from the edges to the cen­ter of the deposit, vary­ing from 30% to 96%, with an aver­age of 62%. Cur­rent­ly, three enter­pris­es oper­ate with­in the explored reserves: OJSC Zakarpat­nerud­prom, SE Sokyrnytske Zeo­lite Plant and SE Zakarpattsky Zeo­lite Plant. In 2020, 334 thou­sand tons of raw mate­ri­als were mined, cov­er­ing the domes­tic demand for zeo­lites in Ukraine, which varies from 1.5 to 3.7 mil­lion tons annu­al­ly. Demand from poten­tial for­eign con­sumers is esti­mat­ed at 4 mil­lion tons per year. Only Geor­gian deposits can com­pete, but their qual­i­ty is infe­ri­or to Ukrain­ian ones.

Use of zeolites

Nat­ur­al zeo­lites have wide and diverse uses in many indus­tries due to their unique adsorp­tion, ion-exchange and cat­alyt­ic prop­er­ties. They are envi­ron­men­tal­ly friend­ly mate­ri­als that are active­ly used in indus­try, agri­cul­ture, con­struc­tion and med­i­cine.

Main areas of appli­ca­tion:

• Water and air purifi­ca­tion. Zeo­lites effec­tive­ly remove harm­ful sub­stances such as heavy met­als, radionu­clides, ammo­nia and phos­phates from water. They are used in water sup­ply sys­tems, waste­water and air fil­tra­tion to absorb pol­lu­tants.
• Agri­cul­ture. Zeo­lites improve soil qual­i­ty due to their ion exchange prop­er­ties, retain­ing ben­e­fi­cial min­er­als and fer­til­iz­ers. They are also used as addi­tives in ani­mal feed, improv­ing diges­tion and pro­mot­ing the elim­i­na­tion of tox­ins from the ani­mal body.
• Build­ing mate­ri­als. Due to their abil­i­ty to sta­bi­lize soils and absorb mois­ture, zeo­lites are used in build­ing mate­ri­als such as cement, con­crete and plas­ters. They improve the strength of mate­ri­als and help reduce mois­ture.
• Petro­chem­i­cals and catal­y­sis. Zeo­lites are impor­tant cat­a­lysts in the petro­chem­i­cal indus­try. They are used in crack­ing process­es to break down hydro­car­bons, allow­ing for more effi­cient pro­cess­ing of oil and nat­ur­al gas.
• Med­i­cine. In med­ical appli­ca­tions, zeo­lites are used as detox­i­fiers, help­ing to remove heavy met­als and tox­ins from the body. They are also being inves­ti­gat­ed for pos­si­ble use in deliv­er­ing drugs to spe­cif­ic cells in the body.

With the grow­ing inter­est in envi­ron­men­tal­ly friend­ly mate­ri­als and tech­nolo­gies, the prospects for the use of nat­ur­al zeo­lites are becom­ing even wider. Some of the pos­si­ble devel­op­ment direc­tions include:

• Ener­gy. Zeo­lites can be used for hydro­gen stor­age and as cat­alyt­ic mate­ri­als in fuel cells. Their abil­i­ty to absorb and store gas­es makes them poten­tial­ly impor­tant com­po­nents for green ener­gy.
• Cli­mate tech­nolo­gies. Zeo­lites can be used in car­bon diox­ide cap­ture and stor­age sys­tems to com­bat cli­mate change. Their abil­i­ty to adsorb CO2 helps reduce green­house gas emis­sions.
• Nan­otech­nol­o­gy and bio­med­i­cine. Nat­ur­al zeo­lites are active­ly stud­ied as car­ri­ers for drug deliv­ery in the body, as well as as com­po­nents for new mate­ri­als with nanos­truc­tures.
• Envi­ron­men­tal clean­ing and reme­di­a­tion. Giv­en the abil­i­ty of zeo­lites to ion exchange, they can be used to clean up radioac­tive and tox­ic pol­lu­tion in areas affect­ed by man-made dis­as­ters.

There­fore, zeo­lites are mul­ti­func­tion­al min­er­als that find appli­ca­tion in var­i­ous indus­tries due to their unique prop­er­ties. Their wide use in envi­ron­men­tal purifi­ca­tion, indus­try and agri­cul­ture makes zeo­lites an impor­tant com­po­nent of mod­ern tech­nolo­gies. Future research and inno­v­a­tive appli­ca­tions will fur­ther expand the pos­si­bil­i­ties of using zeo­lites in the fields of green ener­gy, med­i­cine and envi­ron­men­tal tech­nolo­gies.