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Alkaline by-products as amendments for remediation of historic mine sites
Örebro University, School of Science and Technology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mining has been and still is an important industry in Sweden, it has strongly contributed to the standard of living we have today. Extraction of ore began in the 12th century, but did not come about frequently until the 16th century, which is often seen as the starting age for ore processing and metal extraction. Leaching from sulphidic mine waste deposits is a serious environmental issue. When some of the sulphide minerals come into contact with oxygen they produce acid. Low pH in the waste then promotes leaching of primarily iron and cationic trace elements like copper, zinc and lead and hence affects the surrounding environment by bringing these metals in solution. Mine waste produced today is therefore immediately treated to prevent further oxidation and metal leaching. Cost-effective solutions for the historic mine waste are though still needed, especially as legal responsibilities for the historic waste are in many cases unclear. The historic mine waste is often highly weathered due to long-time exposure to oxygen and water, and also contains higher metal concentrations than modern waste. Also, consideration has to be taken to cultural and historical interests. Covering of the waste is commonly applied for acid rock drainage (ARD) control. By minimizing the oxygen supply, the waste is controlled from further oxidation. Covers can consist of layers of highly impermeable materials or water. Reactive materials (pH-increasing or reducing) can be used as covers or amendments. ARD can also be controlled and treated with reactive barriers and filters. Generally, when neutralizing materials are used for improvement of mine waste or ARD, pure materials such as lime is used. A lot of alkaline by-products in Sweden are deposited as waste and the increasing amount of wastes is also a main environmental problem. The use of alkaline by-products to amend acidic mine waste or ARD therefore both saves natural resources and reduces costs. In the present study, various alkaline by-products have been used in laboratory- and field-scale experiments, either as amendments to historic mine waste or for treatment of ARD. They include: lime mud, green liquor dregs, fly ash, steel slag, lime kiln dust and water works granules. Differences between the alkaline source (carbonate or hydroxide) were shown to be a crucial factor, especially in ARD treatment. Slow dissolution rates for carbonate materials in combination with high iron concentrations resulted in iron precipitation and coating of neutralizing carbonate surfaces. Hydroxide materials was hence found to be superior to carbonate materials in ARD applications and also as solid amendments to oxidized mine waste, in the case where the alkaline material was added as discrete layers. The latter enabled formation of so called hard pans, which work as flow rate reducers and allowing longer contact time with the neutralizing source. Though, when alkaline materials were homogeneously mixed with oxidized mine waste, carbonate materials were able to generate a higher pH and alkalinity, followed by lower trace metal concentrations. Key Words: Oxidized mine waste, lime mud, green liquor dregs, fly ash, lime kiln dust, steel slag, water works granules

Abstract [sv]

Gruvindustrin är sedan länge av stor ekonomisk vikt för Sverige och gruvorna harhaft stor betydelse för vår välfärd även historiskt sett. Av den malm som bryts ärca en fjärdedel järnmalm och tre fjärdedelar sulfidmalm. Vid malmbrytning bildasstora mängder avfall, vilket tas om hand av verksamhetsutövaren som bäransvaret för miljöpåverkan. Läckage från deponier för sulfidhaltigt material kange upphov till omfattande påverkan på den omgivande miljön genom försurningoch spridning av (tung)metaller. För att förhindra försurning täcks vanligtvisavfallet med jord eller vatten. Detta gör man för att förhindra sulfidoxidationsom kan leda till att surt och metallrikt lakvatten transporteras ut från en deponi.I Bergslagen finns ett stort antal historiska gruvområden i behov av åtgärd, dåde kan utgöra ett hot mot både människors hälsa och miljö. Uppskattningsvisfinns gruvavfallsmaterial i storleksordningen varp 3 miljoner m3, sand 14miljoner m3 respektive slagg 1,5 miljoner m3 som är aktuellt för efterbehandling iDalarnas, Västmanlands och Örebros län. Kostnaderna för efterbehandling avdessa områden beräknas uppgå till mellan två och tre miljarder svenska kronor.Äldre avfall skiljer sig i regel från nyproducerat avfall med avseende på avfalletsmetallinnehåll och vittringsgrad samt problem med ansvarsfrågor och frågorrörande kulturhistoriska värden.Vid historisk gruvbrytning (före 1900) fanns inte lika effektiva sorteringsmetoderoch anrikningsprocesser som idag. Således innehåller historisktgruvavfall generellt sett högre metallhalter. Avfall från historiskt gruvavfall harockså varit exponerat för luftens syre, nederbörd och erosion under lång tid.Detta har medfört att en stor andel av det järn som finns närvarande är trevärt(dess oxiderade form), vilket gör att oxidation kan fortgå även om man täckeravfallet.Alkaliska restprodukter från fyra olika branscher, representerade av kalkindustrin,stålindustrin, pappersmassaindustrin samt energiproducentindustrin,har under fyra år studerats för att bestämma deras lämplighet för olika typer avefterbehandlingar av vittrat, surt gruvavfall. Försök har gjorts i labskala, samtstörre pilotskaleförsök, hädanefter benämnda mesoskala. Laboratorie-försökenhar syftat till att utreda neutraliseringspotential, lämpliga inblandningsproportioneroch eventuella metalläckage från de alkaliska materialen. Försökensom gjorts i mesoskala har dels syftat till att studera effekter av att blanda vittrat,sulfidrikt gruvavfall med alkaliska material, så kallade stabiliseringsförsök.Därutöver har försök gjorts med syfte att rena lakvatten från gruvavfall. I detsenare försöket har de alkaliska materialen placerats i 0,4 m3-behållare och surt,metallrikt lakvatten har låtits passera, med pH-ökning och metallfastläggningsom följd.Utifrån resultaten kan vissa av materialen anses ha god förmåga attneutralisera gruvavfallet eller lakvatten från gruvavfallet samt minska utläckageav tungmetaller såsom koppar, zink, kadmium och bly. För dessa materialplaneras i nuläget för fortsatta försök i fullskala. För de material som intefungerat tillfredställande nog för att fortsätta i fullskala kommer ytterligarestudier samt modifikationer av metodiken att utföras, t ex kommer merreducerande förhållanden att försöka uppnås genom att försöksbehållarna täcksmed syreförbrukande material, t ex rötslam.

Place, publisher, year, edition, pages
Örebro: Örebro universitet , 2010. , 108 p.
Series
Örebro Studies in Environmental Science, ISSN 1650-6278 ; 15
Keyword [en]
Oxidized mine waste, lime mud, green liquor dregs, fly ash, lime kiln dust, steel slag, water works granules
Keyword [sv]
Oxiderat gruvavfall, mesakalk, grönlut, flygaska, filterkalk, stålslagg, vattenverksgranuler
National Category
Natural Sciences Environmental Sciences
Research subject
Enviromental Science
Identifiers
URN: urn:nbn:se:oru:diva-11659ISBN: 978-91-7668-750-5 (print)OAI: oai:DiVA.org:oru-11659DiVA: diva2:345976
Public defence
2010-10-08, Örebro universitet, Hörsal Bio, Fakultetsgatan 1, Örebro, 10:15 (English)
Opponent
Supervisors
Projects
Forskningsprojekt: Efterbehandling av gamla gruvavfallsdeponier med hjälp av alkaliska restprodukter. I samarbete med EU-projektet Bergskraft Bergslagen
Available from: 2010-08-30 Created: 2010-08-30 Last updated: 2017-10-18Bibliographically approved
List of papers
1. Mixing of acid rock drainage with alkaline ash leachates: formation of solid precipitates and pH-buffering
Open this publication in new window or tab >>Mixing of acid rock drainage with alkaline ash leachates: formation of solid precipitates and pH-buffering
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Three metal-rich and acidic mine waters (from Bersbo and Ljusnarsberg, Sweden) were mixed with alkaline fly ash leachates in various proportions, representing a pH-titration. The changes in pH, as well as the loss of metals in solution due to precipitation of solid phases, were followed. Mineral equilibria and changes in pH and alkalinity were simulated with the geochemical code PHREEQC using the MINTEQv4 database, and comparisons between measured and simulated pH-responses were made.

The formation of solid precipitates corresponded to fairly well-defined pH-buffering regions, reflecting the composition of the mine waters (notably the levels of Fe, Al and Mn). For the mine waters not dominated by iron the precipitation of zinc had a distinct buffering effect at near-neutral pH. The formation of solid magnesium phases (carbonate, as well as hydroxide) was indicated at high pH (above 9), but no formation of solid calcium phases despite high sulfate levels. The phases that precipitate were various amorphous mixtures, mostly of the metals Fe, Al, Mn, Zn and Mg.

For the iron-rich mine water, pH was poorly simulated with a simple MIX-model, while alkalinity predictions agreed reasonably well with measured data. For the aluminum-rich mine waters the simulated pH-responses agreed well with the measurements.

Keyword
pH-buffering, iron, aluminum, PHREEQC
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12006 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved
2. Mixing of acid rock drainage with alkaline ash leachates: fate and immobilisation of trace elements
Open this publication in new window or tab >>Mixing of acid rock drainage with alkaline ash leachates: fate and immobilisation of trace elements
2011 (English)In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 222, no 1-4, 377-389 p.Article in journal (Refereed) Published
Abstract [en]

Acid rock drainage (ARD) from mine waste dumps often contains ferrous iron, sulphate and high concentrations of trace elements detrimental to the environment. Future costs will be enormous if the problem is not treated today. Simple, low maintenance, cost-effective methods for remediation of historical mine sites are therefore desired. In this study several mine waters were mixed with an alkaline ash leachtes in order to study the fate of the trace elements from both the mine waters (Cd, Cu, Pb, Zn, Ni and Co) and the ash leachates (Cr and Mo). It was found that the addition of ash water will precipitate hydrous ferric oxides (HFO) and hydrous aluminium oxides (HAO) and thereby inducing trace element sorption and co precipitation. It is also clear that the composition of the formed HFO/HAO mix determines the efficiency of the sorption for different trace elements. It is apparent that the amount of precipitating iron will determine the effectiveness of the removal of the trace elements. Sorption occurred much earlier (often one pH unit or more) in the system with high iron concentrations compared to the systems with lower iron concentrations. Removal of cadmium and zinc is difficult below pH 8 if the amount of precipitates is low. Using ash for generation of alkaline water may be a problem with regards to chromium and molybdenum. It is, however, possible to avoid problems with molybdenum by keeping the final pH around 7 and chromium(VI) from the ash water will be reduced into chromium(III) and precipitated as the hydroxide in the presence of iron(II) from the mine waters.

The results imply that it is possible to also use fly ashes in alkaline leach beds in order to neutralize ARD followed by precipitation and sorption of trace elements.

Place, publisher, year, edition, pages
Springer, 2011
Keyword
HFO, HAO, chromium, molybdenum, PHREEQC
National Category
Environmental Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:oru:diva-12007 (URN)10.1007/s11270-011-0831-8 (DOI)000296632900028 ()2-s2.0-80755153691 (Scopus ID)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-12-12Bibliographically approved
3. Laboratory mixing of oxidized mine waste with different alkaline by-products (LD-slag, lime kiln dust and fly ash)
Open this publication in new window or tab >>Laboratory mixing of oxidized mine waste with different alkaline by-products (LD-slag, lime kiln dust and fly ash)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Neutralization and metal removal efficiency were studied for mixtures of alkaline waste materials and oxidized mine waste. Leaching of the mixtures were performed during 65 days at an L/S ratio of 10-18.

It was found that as pH increased the trace element concentrations from the mine waste (mainly Cd, Cu, Pb and Zn) were immobilized through sorption and partly precipitation at higher pH. However, as the amount of alkaline amendments increased leaching of anionic trace elements (Cr, Mo, Se and V) from the alkaline by-products were noticed. For LD leaching of vanadium was particularly significant and showed increasing concentrations with time. It was also found that the anionic trace elements had a maximum leaching at pH around 10-11, where sorption became important. It is thus important to keep pH below 10 in order to minimize the anionic leaching. Optimum pH for immobilization of trace elements from the mine waste was therefore found to be between 8 and 10. Optimum pH can be achieved by addition of around 20-30 % fly ash or by 5-10 % LD or LKD. For the highly alkaline materials there is a significant risk that the resulting pH from a remediation will be higher than 10, which will lead to increased leaching of several anionic trace elements. For the fly ashes the problem is the opposite with risk of obtaining a pH to low to immobilize especially zinc.

Keyword
pH, copper, lead, zinc, vanadium
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12008 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved
4. Chemical stabilization of historic mine waste using alkaline paper mill by-products: batch mixing experiments
Open this publication in new window or tab >>Chemical stabilization of historic mine waste using alkaline paper mill by-products: batch mixing experiments
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Neutralization of acid-generating sulphidic mine waste by mixing with three alkaline paper mill by-products (lime mud, green liquor dregs and fly ash) were studied in batch experiments. An initial liquid/solid (L/S) ratio of 10 was used, where after the mixtures were diluted at four occasions (corresponding to L/S 12, 14, 16 and 18).

pH in the control was 3.3 to 3.1 (slightly decreasing with time/leach day) while pH in the amended systems was increased with three to four pH-units compared to the control. An amendment of 5 % was sufficient to increase pH to 7 and slightly above. A mixture of alkalinities from lime mud and fly ash (carbonate and hydroxide), did not increase pH more than the pure lime mud amendment, except at a very high amendment (50 %).

Trace element immobilizations (Cu, Zn, Cd, Pb) were almost quantitative: Concentrations in amended systems were decreased compared to the control with more than 97 %. Immobilization of lead was pH-dependent, while zinc and copper did not show such strong correlation with pH. The main trace element immobilization mechanism was probably sorption onto formed iron oxy(hydr)oxides and/or coprecipitation.

Elements that might increase due to amendment of the alkaline materials were chromium, vanadium and molybdenum. Chromium was present at highest concentrations in the green liquor dreg, and leaching of chromium (around 600 µg/l) was also observed from this material. Leached chromium concentrations in the green liquor dreg amended systems were however decreased due to lowered pH and Cr(OH)3 precipitation.

Keyword
carbonate neutralization, trace metals, lime mud, green liquor dregs, fly ash
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12009 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved
5. Long-term leaching of fly ash with ARD: pH-dependent accumulation and release of trace elements
Open this publication in new window or tab >>Long-term leaching of fly ash with ARD: pH-dependent accumulation and release of trace elements
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In most ARD treatments, various alkaline sources are used to neutralize the acid produced. Utilization of highly alkaline fly ashes instead of raw materials is a cost-effective alternative, which lately have become increasingly popular.

In laboratory batch experiments, neutralizing capacity for fly ash was studied during 20 days in two parallel series. ARD was added to fly ash once a day, for each increment the liquid to solid ratio (L/S ratio) was increased (final L/S around 3 000).

At an early stage of the experiment (L/S ratio 12), the concentration of barium in solution unexpectedly increased from 200 to 10 000 µg/l. pH showed a slight increase during these observations (pH 12.4-12.7). Furthermore, concentrations of chromium and molybdenum noticeably decreased at these distinct L/S ratios. The decrease of chromium and molybdenum is suggested to be due to incorporation into the interlayer regions of hydrocalumite (Ca4Al2(OH)12(OH)2∙6H2O), replacing the hydroxide groups, which also explain the increase in pH.

Trace elements (Cd, Cu, Pb and Zn) from the added ARD were effectively removed from the solution (93-96 %) and were not released until pH dropped below 7. Major mechanism behind the immobilization of trace elements is sorption onto newly formed HAO/HFO.

Large differences were seen between leaching with different leaching media (distilled water or ARD), why the use of site-specific materials and reagents are crucial in experiments evaluating possible use in field applications.

Keyword
Barium, hydrocalumite, neutralizing capacity
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12010 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved
6. Leaching of lime kiln dust and LD-slag with ARD in a sequential batch experiment
Open this publication in new window or tab >>Leaching of lime kiln dust and LD-slag with ARD in a sequential batch experiment
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Treatment of ARD in a reactive barrier or an alkaline filter prior to release to the recipient is a desired and often suggested alternative. Alkaline candidate materials for the purpose that are cheap are by-products such as fly ash, lime kiln dust and different steel slags. An experiment was carried out where two highly alkaline by-products (LD slag and lime kiln dust) were exposed to a real ARD in sequential batch design.

It was found that the buffering capacity was high enough in both materials in order to neutralize the added ARD even if large portions of the total buffering capacity was washed out during the experiment. Washing out of alkalinity is a greater problem for oxide/hydroxide materials than it is for carbonate dominating materials. Calculations indicated that the buffering capacity in the LKD would last at least until L/S 3 000 while it would last approximately until L/S 1 000 for LD slag. Lack of buffering capacity is thus not the major problem with the materials, but rather the lack of capacity for trace element immobilization. Including sorption onto HFO and HAO and precipitation of different hydroxides and carbonates the already immobilized trace elements from the added ARD started to be remobilized around pH 8. Below pH 8 concentrations increased rapidly due mainly to desorption and was soon found to be higher than in the added ARD.

Some of the divalent elements (Mg and Mn) were also found to be controlled by their hydroxides at high pH and at circumneutral pH by their carbonates. This results in higher concentrations at lower pH (below 10) since the carbonates are more soluble than the hydroxides.

It is important to characterize the used alkaline by-products at the expected chemical conditions in order to be able to assess potential trace element leaching (most likely anionic elements such as vanadium and chromium).

Keyword
HFO, HAO, pH, vanadium, trace elements
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12011 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved
7. Paper mill by-products and fly ash as amendments to oxidized waste rock: neutralization and trace metal reduction in a meso-scale field study
Open this publication in new window or tab >>Paper mill by-products and fly ash as amendments to oxidized waste rock: neutralization and trace metal reduction in a meso-scale field study
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Remediation of oxidized mine waste is often hampered by the risk of reductive dissolution of ferric iron phases and the resulting release of trace elements. In order to partly avoid this problem the oxidized mine waste can be amended with an alkaline material. In this meso-scale experiment with 7 different amended systems and a control an oxidized waste rock was mixed with several alkaline by-products and leachates were collected for 44 months. Results show that pH in the amended systems increased between 1.1 and 2.2 pH units compared to the untreated reference (pH 4.4). The increase in pH resulted in a significant decrease in trace element concentrations, averaging a concentration reduction around 97 %. Sorption was probably the main reduction mechanism.

Flow rate measurements in the different systems showed a strong correlation between pH and the flow rate. It was concluded that the type of alkaline material and the number of alkaline layers were of less importance than the flow rate when it came to quality of the leachates. However, fly ashes were found in all the best performing systems. Longer residence time clearly improves the quality of the leachates. When it comes to comparison of the different systems it seems that systems containing fly ashes performed best. Least effective systems contained green liquor dregs and amendments with too little fly ash. It is clear that alkaline materials can be used in order to reduce the leaching of trace elements from historical mine waste deposits.

Keyword
lime mud, green liquor dreg, fly ash
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12012 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved
8. Successive neutralization, precipitation and trace metal immobilization in meso-scale filters for ARD treatment
Open this publication in new window or tab >>Successive neutralization, precipitation and trace metal immobilization in meso-scale filters for ARD treatment
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Six alkaline by-products were studied in reactive filters (3×0.4 m3) built on the historic mine site Ljusnarsbergsfältet, Kopparberg, Sweden. Each filter was made out of three connected sections in a sequence (neutralization – oxidation (precipitation) – sorption). Total buffering capacity of the alkaline materials was found to have a minor impact on their respective performances. Other chemical and physical circumstances were more important, e.g. carbonation, iron precipitation and preferential flow path formations. A combination of fresh fly ash and lime mud had similar chemical responses as a carbonated fly ash. These filters were also the worst performers, considering overall trace element immobilizations.

No particular differences were found between two different passive adsorbents in the oxidation stage, where iron and aluminum were intended to precipitate and act as sorbent phases for other elements: Cu, Zn, Cd, and Pb. In general it was found that highly alkaline materials containing alkalinities as CaO/Ca(OH)2 were superior to materials with carbonate alkalinity.

Keyword
lime mud, fly ash, green liquor dreg, lime kiln dust, LD-slag, water works granules
National Category
Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-12013 (URN)
Available from: 2010-10-05 Created: 2010-10-05 Last updated: 2017-10-17Bibliographically approved

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