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Da bi se dobila kvarcna sirovina koja svojom kvalitetom udovoljava specifičnim zahtjevima pojedinih industrija, rovni pijesak mora proći odgovarajući proces oplemenjivanja. Mogućnost dobivanja koncentrata kvarcnog pijeska odgovarajuće kvalitete ovisi o značajkama rovnog pijeska, u prvom redu o vrsti i sadržaju mineralnih primjesa u pijesku, te značajkama primjenjenih oplemenjivačkih postupaka. Kada se primjese javljaju u obliku oksidnih prevlaka na površini kvarcnih zrna, primjenjuje se atricijsko čišćenje. Odstranjivanjem oksidnih prevlaka, kvaliteta pijeska značajno se može poboljšati. S ciljem utvrđivanja mogućnosti oplemenjivanja kvarcnog pijeska perspektivnih hrvatskih ležišta (“Vrtlinska”, “Štefanac” i “Španovica”) i postizanja koncentrata čija kvaliteta ispunjava zahtjeve domaće industrije, provedena su laboratorijska ispitivanja s tri različita uzorka rovnog pijeska. Ispitivanjima su utvrđene osnovne značajke (granulometrijski, kemijski i mineralni sastav) rovnih uzoraka kvarcnog pijeska, te mogućnost poboljšanja njihove kvalitete primjenom postupaka pranja, klasiranja i mehaničkog atricijskog čišćenja., To meet high quality requirements defined for specific industrial applications, the raw sand often has to be subjected to extensive physical and chemical processing. The possibility of achieving silica sand concentrate of required quality depends mostly on raw sand properties, primarily mineral impurity types and contents, and features of applied beneficiation methods. When the impurities occur in the form of oxide coatings on the surfaces of the single sand grains, attriton scrubbing is applied. By reducing the proportion of oxide coatings on the grains, the quality of sand can be improved. With the aim to determine the possibilities of the beneficiation of silica sand from significant Croatian deposits (“Vrtlinska”, “Štefanac” and “Španovica”) and achieve concentrate grade complying with the requirements of domestic industry, laboratory tests were conducted on three raw sand samples with different SiO2 and impurity contents. Grain size distribution, chemical and mineral composition of raw sand samples, and the possibility of their quality improvement by applying the washing, classification and attrition scrubbing were defined by analysis of test results.

Silica sand is an important non-metallic mineral raw material within the resources of the Republic of Croatia. Croatian silica sand reserves could meet industrial needs over the long term. The 15 exploitation fields are registered, and the average annual production in the last 10 years is about 240, 000 tonnes. Depending on quality i.e. specific physical and chemical properties (grain size distribution, chemical and mineral composition, moisture content, etc.), silica sand is used as the basic mineral raw material for many industrial applications. To meet defined chemical and physical specifications according to intended application, the raw sand often has to be subjected to extensive physical and chemical processing. The paper describes main beneficiation methods used in the processing of sand intended for industrial uses. Beneficiation procedure applied at the silica sand deposit "Jerovec" located in north-western Croatia is presented, as well as the results achieved under field conditions.

Kvarcni pijesak je sirovina sa širokim spektrom primjena od kojih su najpoznatije primjene u industriji stakla i građevinarstvu. Republika Hrvatska raspolaže s potvrđenim rezervama od oko 40 milijuna tona i dugom tradicijom eksploatacije koja se posljednjih godina odvija smanjenim kapacitetom. Prosječna godišnja proizvodnja rovnog kvarcnog pijeska u Hrvatskoj iznosi oko 150 tisuća tona. Eksploatacija kvarcnog pijeska sastoji se od dobivanja rovnog kvarcnog pijeska strojnim iskopom na površinskim kopovima te oplemenjivanja u oplemenjivačkom postrojenju u svrhu daljnjeg plasmana na tržište (industriju). U ovom radu analizira se životni ciklus kvarcnog pijeska od dobivanja na površinskom kopu do ulaza u tvornicu stakla. U tu svrhu dizajnirano je sedam varijanti (alternativa) eksploatacije kvarcnog pijeska s razlikama u oplemenjivačom procesu, dok je osma varijanta generička, kreirana isključivo korištenjem Ecoinvent baze podataka. Za potrebe projektiranja varijanti generirana je baza podataka s kapacitetima rudarskih strojeva i opreme korištenjem kataloga i specifikacija proizvodača koji su postavljeni na Internetu. Dobiveni rezultati i normativi varijanti uspoređeni su s podacima na terenu kako bi se provjerila njihova reprezentativnost. Procjena utjecaja i grafički prikaz podataka provedeni su uz pomoć programa Sima Pro. Za procjenu utjecaja odabrana je metoda ReCiPe u kojoj se utjecaji na okoliš izražavaju pomoću osamnaest indikatora srednje točke koji se zatim preko mehanizama okoliša prevode na razinu krajnje točke utjecaja, a to su štetni utjecaji na ljudsko zdravlje, ekosustave i troškove proizvodnje resursa (zbog npr. smanjenja njihove dostupnosti). Rezultati indikatora krajnje točke za kategorije utjecaja na ljudsko zdravlje, ekosustave i povećanje ukupne godišnje cijene resursa su pokazali kako u oplemenjivanju kvarcnog pijeska najjednostavniji postupci kao što su pranje i klasiranje imaju najmanje utjecaje. Uz uvjet da su ispuštanja toksičnih tvari iz procesa oplemenjivanja u sastavnice okoliša onemogućena ili svedena na minimum, presudan utjecaj na okoliš medu alternativama ima potrošnja vode. Promatrano od dobivanja rovnog pijeska na površinskom kopu, preko transporta i oplemenjivanja kvarcnog pijeska, korištenje fosilnih goriva pokazalo se kao najvažniji čimbenik utjecaja na okoliš cradle-to-gate dijela životnog ciklusa kvarcnog pijeska. Korištenje električne energije nije se pokazalo značajnim u pogledu izravnih utjecaja, ali svakako doprinosi utjecajima neposredno, preko proizvodnje električne energije. Transport mokrog pijeska vlažnosti 6% (mas.) i sušenje otpadnom toplinom u tvornici stakla pokazala se kao bolja opcija nego sušenje pijeska do vlažnosti manje od 1% u pogonu za oplemenjivanje i transport do tvornice stakla., Introduction: Silica sand or quartz sand is mineral resource with wide varieties of applications; glass industry and construction are the most common example. Republic of Croatia has confirmed reserves of 40 million tons and long tradition of exploitation and processing. Average production of raw silica sand in Croatia is 150 thousand tons. This paper defines the procedure for life cycle assessment of silica sand exploitation and processing and gives a model of quartz sand life cycle. Environmental profiles of different processing options are calculated, and included in cradle to gate life cycle study of silica sand for glassmaking industry. Based on environmental profiles of different options, key segments of production process are identified and ranked. A guideline for choice of technology that includes direct and indirect environmental impacts at design level is given. Materials and methods. In this research eight alternatives of silica sand production process are designed. For the purpose of design, equipment and machinery database is generated. Designed inputs and outputs in production processes are checked for consistency with industry data. Life cycle assessment is performed using Sima Pro software. Life cycle impact assessment is performed using ReCiPe midpoint and endpoint method. Analyzed alternatives are: • Alternative 1: Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; drying; electrostatic separation of feldspar, magnetic separation of magnetic minerals; road transport of dried silica sand (water content less than 1% mass) using lorry (truck) on transporting distance 100 km. • Alternative 2-1: Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; road transport of wet silica sand (water content 6% mass) using lorry (truck) on transporting distance 100 km; drying in glass plant using waste heat. • Alternative 2-2: Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; drying; road transport of dried silica sand (water content less than 1% mass) using lorry (truck) on transporting distance 100 km. • Alternative 3-1. Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; flotation of mica, heavy minerals and feldspar; road transport of wet silica sand (water content 6% mass) using lorry (truck) on transporting distance 100 km; drying in glass plant using waste heat. • Alternative 3-2. Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; flotation of mica, heavy minerals and feldspar; drying; road transport of dried silica sand (water content less than 1% mass) using lorry (truck) on transporting distance 100 km. Alternative 4-1. Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; gravitation concentration of quartz; road transport of wet silica sand (water content 6% mass) using lorry (truck) on transporting distance 100 km; drying in glass plant using waste heat. • Alternative 4-2. Surface exploitation (excavation) using bulldozers; transportation from excavation site to processing plant (3 km) using dumpers; washing and sizing; gravitation concentration of quartz; drying; road transport of dried silica sand (water content less than 1% mass) using lorry (truck) on transporting distance 100 km. • Alternative 5. Simulation of surface exploitation and mineral processing outside the Croatia (data for sand production in Switzerland) and silica sand import by railroad transport on distance 700 km using EcoInvent database Among the analyzed alternatives the following alternatives have shown the smallest impact: “5” (simulation based on Ecoinvent data); “2-1” (silica sand production from high quality raw sand utilizing simple processing techniques such as sizing and washing ); “2-2” (silica sand production from high quality raw sand utilizing simple processing techniques such as sizing and washing plus drying in the rotary drier); “4-1” (silica sand production utilizing processing techniques such as sizing, washing and gravity concentration); “3-1” (silica sand production utilizing processing techniques such as sizing, washing and froth flotation). Intermediate impact have shown the alternatives “1” (silica sand production utilizing processing techniques such as sizing, washing, drying with grain surface conditioning using hydrofluoric acid, and electrostatic separation) and “4-2” (silica sand production utilizing processing techniques such as sizing, washing, gravity concentration and drying). The highest impact has shown the alternative “3-2” (silica sand production utilizing processing techniques such as sizing, washing, flotation and drying). Process contribution analysis has shown the major contribution following from using fossil fuels and water. Conclusion and recommendations. In silica sand processing the simplest mineral processing methods such as sand washing and classifying have the smallest impacts. When emissions of chemicals to environment are prevented or minimal, deciding factor between the processing alternatives has the water consumption. Second factor affecting significantly the environmental performance in silica sand processing is the fossil fuel use. In cradle-to-gate production process (including silica sand exploitation, processing and transportation) the fossil fuel use (and production) has the major impact on environment. Damage from electricity use (and production) is considerably lower. Transportation of naturally dried wet sand (w=6%) and drying using waste heat in glass factory is better option than drying in processing plant and then transporting it into the glass factory. Recommendations for lowering the environmental impact of silica sand at different production stages: • In surface mining: lowering the diesel consumption using mining machinery with good fuel efficiency per ton of produced sand and utilization of mining machinery with continuous working regime instead of cyclic (e.g. rotary or bucket excavator instead of bulldozer); • In sand washing and wet classifying: the use of efficient water collection, regeneration and recirculation systems • In flotation: the use of flotation reagents that can be easily separated from water (based on their phase) and/or recirculated back into the process. • In electrostatic separation: the use of highly efficient drying system. • In drying: lowering the fossil fuel consumption; utilizing as much as possible the gravitational dewatering and natural evaporation; drying using waste heat or other heat sources that cause less damage than fossil fuels.