Analysis of the mechanism of acid mine drainage neutralization using flotation tailing and fly ash

[N. Petronijević]

126 listova

Inženjerstvo zaštite životne sredine / Environmental Engineering

U doktorskoj disertaciji su predstavljeni rezultati istraživanja primene otpadnih sirovina, flotacijske jalovine i letećeg pepela, za neutralizaciju kisele rudničke vode sa jasnim definisanjem mehanizma odvijanja samog postupka. Kao alternativni agensi za neutralizaciju kisele rudničke vode jezera „Robule“ (pH 2,47) korišćeni su flotacijska jalovina iz rudnika bakra Majdanpek (FJM) i pepeo sa dve lokacije: termoelektrana „Nikola Tesla”-Obrenovac (EF) i termoelektrana „Kostolac” (KOST). U okviru fizičko-hemijske karakterizacije polaznih uzoraka flotacijske jalovine FJM i pepela EF i KOST određen je hemijski i mineraloški sastav uz ispitivanje stepena lužljivosti i stabilnosti otpadnih materijala testovima definisanim zakonom za ove postupke, TCLP (Toxicity Characteristic Leaching Procedure), EN 12457-4 i testa za utvrđivanje kapaciteta neutralizacije kiselosti ANC testa. Utvrđeno je da se radi o baznim materijalima koji poseduju značajan kapacitet neutralizacije kiseline i zato predstavljaju veoma efikasno alternativno sredstvo za neutralizaciju kiselih rudničkih voda i uklanjanje prisutnih metala. Za simulaciju vodenog tretmana agensima za neutralizaciju FJM, EF i KOST korišćen je program PHREEQC i dobijeni rezultati su predstavljeni u obliku indeksa zasićenja (SI) odgovarajućih mineralnih faza, koji su promenili vrednost pri specifičnim vrednostima pH. Rezultati su pokazali da je postupkom neutralizacije sa FJM istaloženo više od 99% Al, Fe i Cu, 98% Pb i 92% Zn. Koncentracije Cd i Mn su povećane u rastvoru usled ispiranja ovih metala iz flotacijske jalovine. Da bi se koncentracija Mn smanjila ispod dozvoljenih granica ispuštanja, urađen je dodatni tretman primenom hidratisanog kreča kako bi se pH povećao do 10 i tako obezbedili uslovi za njegovo uklanjanje. Rezultati su pokazali da se FJM može primeniti u aktivnom tretmanu kiselih rudničkih voda u kombinaciji sa hidratisanim krečom. Čvrsti ostatak flotacijske jalovine FJM7d, nakon neutralizacije AMD, ima visoku koncentraciju S i povećan sadržaj teških metala koji su se istaložili u obliku hidroksida tokom postupka neutralizacije. Nakon neutralizacije kiselih rudničkih voda (AMD-Acid Mine Drainage) primenom FJM, čvrsti ostatak ima za oko 4 % više čestica čije su dimenzije manje od 63 μm, dok se sadržaj čestica krupnoće iznad 250 μm smanjuje. Ovome idu u prilog i izmerene vrednosti zapreminske gustine pre, 1,21 g/cm3 i posle, 1,17 g/cm3 AMD tretmana. Ovi podaci su ukazali da je postupak luženja praćen usitnjavanjem karbonata tokom tretmana. Zbog koncentracije Sb od 24 mg/kg, prema EN 12457-4 testu, FJM pre tretmana se klasifikuje kao opasan otpad, jer je maksimalna dozvoljena koncentracija 5 mg/kg Sb. Međutim, FJM7d, kao čvrsti ostatak nakon tretmana je u kategoriji neopasnog otpada, jer sadrži 0,7 mg/kg Sb. Za antimon u zakonskoj regulativi Republike Srbije ne postoje definisane granične vrednosti za efluent. Na osnovu sva tri testa luženja TCLP testa, EN 12457-4 testa i testa dugotrajnog luženja snegom rezultati FJM7d pokazuju koncentracije opasnih elemenata znatno ispod propisanih granica. Laboratorijska ispitivanja su potvrdila da se pepeo EF i KOST mogu primeniti u postupku neutralizacije kisele rudničke vode jezera „Robule“. Rezultati su pokazali da je postupkom neutralizacije sa letećim pepelom EF i KOST istaloženo više od 99% Al, Fe i Cu i Zn i 89% Pb. Iako pripadaju istoj klasi pepela, prikupljeni uzorci su pokazali značajne razlike u mineralnom sastavu koji vode različtim mogućnostima za neutralizaciju kiselih rudničkih voda. Mehanizam neutralizacije kod letećeg pepela se svodi na uklanjanje Fe3+ i Al3+ jona i formiranje nerastvorljivih (oksi)hidroksidnih jedinjenja, koje se dešava u prvih 5 minuta neutralizacije, pri pH 4,38 za EF uzorak i 5,15 za uzorak KOST i stvara povoljne uslove za koprecipitaciju ostalih metala u tragovima (Cu, Zn, Ni, Pb i Cd) iz AMD-a, što je dodatno poboljšano adsorpcijom katjona na česticama letećeg pepela. Takođe je sprovedena i uporedna analiza neutralizacije kiselih rudničkih voda alternativnim i konvencionalnim sredstvom za neutralizaciju. Faktori koji utiču na pH i prirodu konačno dobijenog rastvora AMD su količina pepela ili jalovine u odnosu na AMD, količina hidrolizujućih sastojaka dostupnih u AMD i vreme trajanja reakcije. Na osnovu rezultata EN 12457-4 testa pepeo EF i KOST koji su korišćeni za neutralizaciju kisele rudničke vode jezera „Robule“, se svrstavaju u kategoriju opasnog otpada zbog povećanog sadržaja Sb. Koncentracije ostalih elemenata u rastvoru za luženje su znatno ispod propisanog nivoa TCLP i EN12457-4 testova. Kako bi se ispitala stabilnost metala i njihova mobilnost pri padavinama na samom mestu deponovanja, primenjen je dugotrajni test luženja otopljenim snegom. Cilj primene ovog testa jeste simulacija uslova na samom terenu izlaganjem pepela dugotajnom uticaju padavina (otopljeni sneg) u laboratoriji. Rezultati dugotrajnog testa su pokazali smanjenje Sb u uzorku pepela i mogućnost mobilnosti antimona u životnu sredinu izlaganjem padavinama, pa je pepeo i posle tretmana otopljenim snegom zadržao kategoriju opasnog otpada. Kao krajnji rezultat neutralizacije kisele rudničke vode jezera „Robule“ primenom alternativnih agenasa flotacijske jalovine i letećeg pepela dobijena je prečišćena voda koja je bezbedna za ispuštanje u životnu sredinu, što je i bio cilj.

This doctoral dissertation presents the experimental findings of using waste raw materials, flotation tailings, and fly ash from coal combustion to neutralize acid mine water, as well as the mechanism of neutralization. Alternative resources for neutralizing acid mine water of Lake Robule included flotation tailing from the copper mine Majdanpek (FJM) and fly ash from two power plants: „Nikola Tesla“– Obrenovac (EF) and „Kostolac“ power plant (KOST) (pH 2.47). The chemical and mineralogical composition of the initial samples of flotation tailing FJM and fly ash EF and KOST was evaluated by assessing leaching and stability of samples using two standard leaching tests: TCLP (Toxicity Characteristic Leaching Procedure )and EN 12457-4, as well as the ANC (Acid Neutralization Capacity) test. These base materials were shown to have a large capacity to neutralize acid, making them a highly effective alternative material for neutralizing acid mine drainage and eliminating metals. The software PHREEQC was used to model the aqueous speciation of FJM, EF, and KOST neutralizing agents, and the results were presented as saturation index (SI) of the corresponding mineral phases, formed during the treatment of lake water with flotation tailings and fly ash based on pH and element concentrations in the solutions. The FJM neutralization experiment precipitated more than 99 percent of Al, Fe, and Cu, 98 percent of Pb, and 92 percent of Zn, according to the findings. Leaching of these metals from flotation tailings raises Cd and Mn concentrations. Additional treatment was undertaken using hydrated lime to boost the pH to 10 and so offer circumstances for its removal, in order to reduce the concentration of Mn below the authorized limits by Serbian legislation. FJM can also be used safely in the active treatment of acid mine waters when combined with hydrated lime, according to the findings. FJM7d, the solid residue of flotation tailings following AMD (Acid Mine Drainage) neutralization, has a high concentration of S and a higher quantity of heavy metals that precipitated in the form of their hydroxides during the neutralization process. The solid residue has around 4% more particles with dimensions smaller than 63 m after AMD neutralization with FJM, but the concentration of particles larger than 250 m decreases. The measured bulk density values before and after AMD treatment, 1.21 g / cm3 and 1.17 g / cm3, support this. These findings suggested that during treatment, the leaching process was followed by carbonate comminution. According to the EN 12457-4 test, FJM before treatment is categorized as hazardous waste due to the Sb concentration of 24 mg/kg, because the maximum allowable value is 5 mg/kg Sb. FJM7d, on the other hand, is classified as non- hazardous waste as a solid residue after treatment because it contains 0.7 mg/kg Sb. There are no defined effluent limit values for antimony in the legislation of the Republic of Serbia. FJM7d results demonstrate hazardous element concentrations substantially below the allowed limits in all three tests, TCLP leaching tests, EN 12457-4 test, and long-term melted snow leaching test. Long-term leaching with melting snow had the goal of simulating environmental conditions in the lab for a year. The results of the normal leaching techniques were compared to the results of the obtained drainage water. Laboratory tests have demonstrated that fly ash EF and KOST can be used to neutralize acid mine water from Lake „Robule“. The EF and KOST neutralization experiment precipitated more than 99 percent of Al, Fe, and Cu, and Zn and 89 percent of Pb, according to the findings. Both neutralization materials, flotation tailing and fly ash, due to their basic character, lead to increasing of pH. Although both ashes belong to the so-called F class of fly ash, collected samples showed significant differences in mineral composition that lead to different possibilities for neutralization of acidic mine waters. The removal of Fe3+ and Al3+ ions and formation of insoluble (oxy)hydroxide compounds, that happens in first 5 minutes of neutralization, at pH 4.38 for EF sample and 5.15 for the KOST sample creates favourable conditions for co-precipitation of other trace metals (Cu, Zn, Ni, Pb, and Cd) from AMD, which is further enhanced by cation adsorption on fly ash particles. The amount of ash added to the neutralization process, the amount of hydrolyzing chemicals accessible in AMD, and the duration of the neutralization process all influence the pH and chemical composition of the final purified AMD solution. Due to the increasing level of Sb, the ash EF and KOST used for neutralization of acid mine water in Lake Robule are classed as hazardous waste based on the findings of the EN 12457-4 test. Other element concentrations in the leaching solution are much lower than the TCLP and EN12457-4 test requirements. Leaching with melting snow was used to assess the leaching of Sb under outdoor circumstances and its mobility. The amount of Sb in the ash was lowered, which suggests that Sb can be removed from the environment by leaching with precipitation, keeping the ash in the hazardous waste category. The purpose of this dissertation was to produce purified water that was safe for release into the environment as a result of the neutralization of the acid mine water of Lake „Robule“ utilizing alternative materials such as flotation tailings and two fly ash.

isele rudničke vode, flotacijska jalovina, leteći pepeo, smanjenje otpada, tretman kiselih rudničkih voda, neutralizacija, alternativni materijali za neutralizaciju kiselih rudničkih voda

Acid Mine Drainage (AMD), flotation tailing, fly ash, wate minimization, Acid mine drainage treatment, neutralization, alternative materials for AMD neutralization

669.053.4.094.8:504.5(043.3)

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