Search

The production of nonmetallics in Croatia highly exceeds the production of any other mineral raw material. Zagreb, capital of Croatia, is the biggest consumer of sand, gravel and crushed rock aggregates. Since listed materials, due to their low cost, don’t bear long transport, nearby Zagreb numerous quarries and gravel-pits were opened. An overview of sand and gravel production in Croatia is given in this paper. The technology of gravel extraction and dressing are shown on the example of Novo Čiče gravel-pit, together with geological structure of surrounding area and the properties of extracted gravel.

U ovom radu prikazani su rezultati ispitivanja koncentracije kvarcnog pijeska postupcima gravitacijske koncentracije (koncentracijskim stolom i spiralnim žlijebom – Humphreysovom spiralom). Cilj rada je ispitati mogućnost koncentracije kvarcnog pijeska gravitacijskom koncentracijom uz postizanje kvalitete koncentrata koji zadovoljava uvjete kvalitete za plasiranje na tržište. Provedena su dva seta ispitivanja na koncentracijskom stolu pri različitim nagibima koncentracijskog stola (3°, 6° i 9°), jedan s ciljem postizanja što veće kvalitete koncentrata i jedan s ciljem postizanja što većeg masenog iskorištenja. Ukupno je napravljeno ispitivanje na 6 uzoraka kvarcnog pijeska na koncentracijskom stolu. Na spiralnom žlijebu provedena su 4 ispitivanja pri različito podešenim parametrima (otvori ispusta za tešku frakciju, gustoća suspenzije i protok ispirne vode). Uspoređeni su tehnološki pokazatelji uspješnosti koncentracije pojedinih ispitivanja, odnosno postignuta kvaliteta koncentrata utvrđena kemijskom analizom uspoređena je s uvjetima kvalitete za plasiranje na tržište., This thesis presents the results of concentration tests carried out on quartz sand using gravity concentration methods (shaking table and spiral concentrator – Humphreys spiral). The aim of the thesis is to examine the possibility of concetrating quartz sand using gravity concentration methods to achieve concentrate quality that satisfies the quality requirements of the marketplace. Two sets of tests were carried out using a shaking table at different shaking table inclination (3°, 6° i 9°), one set aiming to achieve higher concentrate quality and the other set aiming to achieve higher recovery. Tests were carried out on 6 samples of quartz sand using shaking the table. Using a spiral concentrator, 4 tests were carried out with different parameter (heavies openings, slurry density and wash water flow) adjustment. The concentration efficiency indicators of each test were compared i.e. achieved concentrate grades determined by chemical analysis were compared with the quality requirements for market placement.

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.