9 research outputs found
Kaivosten jÀtevakuuden alan laajentamisen ympÀristönsuojelullinen vaikuttavuus ja kustannukset
Kaivosten jÀtevakuuden alan laajentamisen ympÀristönsuojelullinen vaikuttavuus ja kustannuksetHankkeen taustalla on hallitusohjelman kirjaus kaivosten ympÀristönsuojelun parantamisesta muun ohella vakuussÀÀntelyÀ kehittÀmÀllÀ. Nykytilanteessa vakuussÀÀntely ei kata useita olennaisia vesijakeita ja niihin liittyviÀ vastuita, kuten louhosten ylivuotovesien hallintaa. Hankkeessa tuotettiin tietoa kaivoksilla syntyvien vesijakeiden mÀÀrÀstÀ ja laadusta sekÀ kaivosten vesienhallinta- ja kÀsittelytekniikoista, tarkkailusta ja lopettamis- ja jÀlkihoitovaiheen kustannuksista. Hankkeessa tuotettiin myös tietoa tekijöistÀ, jotka vaikuttavat vesijakeiden ominaisuuksiin, vesienkÀsittelytavan valintaan, tarkkailuun ja kustannuksiin.
Hankkeessa analysoitiin myös vakuussÀÀntelyn nykytila katvealueineen kaivosten vesienhallinnan, vesienkÀsittelyn ja ympÀristötarkkailun nÀkökulmista sekÀ kehitettiin sÀÀntelymalli nÀihin vastaamiseksi. SÀÀntelymallissa YSL:n mukaisen vakuuden ala laajenisi jÀtteiden kÀsittelytoiminnasta koko kaivostoimintaan. Malliin sisÀltyisi sÀÀntelyÀ kaivostoiminnan sulkemissuunnitelmasta, vesienhallinta- ja vesienkÀsittelysuunnitelmasta, seuranta- ja tarkkailusuunnitelmasta sekÀ uudesta kaivostoiminnan vakuudesta. Vakuuden laajentamisen taloudellisen merkityksen suuruusluokka voi yksittÀisellÀ kaivoksella jÀÀdÀ pienimmillÀÀn alle sadantuhannen. Suurimmillaan, lÀhinnÀ ÀÀritapauksissa, lisÀkustannukset voivat olla kymmenen miljoonan suuruusluokkaa.TÀmÀ julkaisu on toteutettu osana valtioneuvoston selvitys- ja tutkimussuunnitelman toimeenpanoa (tietokayttoon.fi). Julkaisun sisÀllöstÀ vastaavat tiedon tuottajat, eikÀ tekstisisÀltö vÀlttÀmÀttÀ edusta valtioneuvoston nÀkemystÀ
Experimental and computational studies on sulphate removal from mine water by improved lime precipitation
Abstract
Lime precipitation has been used for the treatment of mine water for decades; however, the impact of precipitation conditions is not adequately known. In this thesis, four aspects related to the removal of sulphate from mine water by lime precipitation are considered: the effect of magnesium on lime precipitation, the utilisation of by-products in lime precipitation, enhancement of lime precipitation, and utilisation of the precipitate.
Sulphate removal in the presence of magnesium at the commonly used lime precipitation treatment pH of 9.6 was found unefficient as magnesium was keeping the sulphate soluble in the form of magnesium sulphate. At higher treatment pH of 11.5, magnesium that was naturally present in the mine water was shown to precipitate as magnesium hydroxide, which could serve as seed crystals for gypsum or co-precipitate sulphate thus enhancing sulphate removal.
Quicklime manufacturing generates by-products that, currently, have few applications. The by-products examined in this study were successfully applied for mine water neutralization replacing commercial lime products. These by-products were found to remove sulphate equally well from the mine water. However, differences between by-products were observed in the consumption, and produced sludge quantities and qualities.
An enhanced lime precipitation method is the precipitation as ettringite, which was used to reduce the sulphate content in mine water to less than the value set as the drinking water guideline in Finland. Furthermore, the formed precipitate was found to remove arsenate from the model solution.TiivistelmÀ
Vaikka kalkkisaostusta on kÀytetty kaivosten vesienkÀsittelyyn useiden vuosikymmenten ajan, tieto olosuhteiden vaikutuksesta kÀsittelyn tehokkuuteen sulfaatin poiston osalta on puutteellista. TÀmÀ vÀitöskirja kÀsittelee sulfaatinpoistoa kaivosvesistÀ kalkkisaostuksen avulla neljÀllÀ eri osa-alueella: magnesiumin vaikutus kalkkisaostukseen, kalkinpolton sivutuotteiden hyödyntÀminen kalkkisaostuksessa, kalkkisaostuksen tehostaminen ja muodostuvan saostuman hyödyntÀminen.
Magnesiumin todettiin kokeellisesti ja laskennallisesti haittaavan sulfaatin poistoa kaivosvedestÀ kalkkisaostuksessa yleisesti kÀytetyssÀ pH:ssa 9.6 pitÀmÀllÀ sulfaattia liukoisessa muodossa magnesiumsulfaattina. Korkeammassa pH:ssa 11.5 puolestaan kaivosveden luontaisesti sisÀltÀmÀn magnesiumin havaittiin kokeellisesti ja laskennallisesti saostuvan magnesiumhydroksidina, joka voi toimia siemenkiteinÀ kipsille tai kerasaostaa sulfaattia ja siten tehostaa sulfaatin poistoa.
Kalkinpolton sivutuotteina muodostuu jakeita, joille ei tÀllÀ hetkellÀ ole juurikaan kÀyttökohteita. TÀssÀ työssÀ kÀytettiin kalkinpolton sivutuotteita korvaamaan kaupallista kalkkia kaivosveden neutraloinnissa. Sivutuotteet poistivat sulfaattia yhtÀ tehokkaasti kuin kaupalliset kalkkituotteet. Sivutuotteiden vÀlillÀ havaittiin eroja niiden kulutuksessa sekÀ muodostuvan lietteen mÀÀrÀssÀ ja laadussa.
Saostuksella ettringiittinÀ, joka on tehostettu versio perinteisestÀ kalkkisaostuksesta, saavutettiin sulfaattipitoisuuden lasku alle Suomessa juomavedelle kÀytetyn suositusarvon. LisÀksi havaittiin muodostuneen ettringiittisaostuman olevan potentiaalinen materiaali arsenaatin poistoon vedestÀ
Phosphate and Ammonium Removal from Water through Electrochemical and Chemical Precipitation of Struvite
Batch electrocoagulation (BEC), continuous electrocoagulation (CEC), and chemical precipitation (CP) were compared in struvite (MgNH4PO4·6H2O) precipitation from synthetic and authentic water. In synthetic water treatment (SWT), struvite yield was in BEC 1.72, CEC 0.61, and CP 1.54 kg/m3. Corresponding values in authentic water treatment (AWT) were 2.55, 3.04, and 2.47 kg/m3. In SWT, 1 kg struvite costs in BEC, CEC, and CP were 0.55, 0.55, and 0.11 €, respectively, for AWT 0.35, 0.22 and 0.07 €. Phosphate removal in SWT was 93.6, 74.5, and 71.6% in BEC, CEC, and CP, respectively, the corresponding rates in AWT were 89.7, 77.8, and 74.4%. Ammonium removal for SWT in BEC, CEC, and CP were 79.4, 51.5, and 62.5%, respectively, rates in AWT 56.1, 64.1, and 60.9%. Efficiency in CEC and BEC are equal in nutrient recovery in SWT, although energy efficiency was better in CEC. CP is cheaper than BEC and CEC
Removal of metals by sulphide precipitation using NaâS and HSâ»-solution
Abstract
Precipitation of metals as metal sulphides is a practical way to recover metals from mine water. Sulphide precipitation is useful since many metals are very sparingly soluble as sulphides. Precipitation is also pH dependent. This article investigates the precipitation of metals individually as sulphides and assesses which metals are precipitated as metal hydroxides by adjustment of the pH. The precipitation of different metals as sulphides was studied to determine the conditions under which the HSâ» solution from the sulphate reduction reaction could be used for precipitation. HâS gas and ionic HSâ» produced during anaerobic treatment could be recycled from the process to precipitate metals in acidic mine drainage (AMD) prior to anaerobic treatment (Biological sulphate reduction), thereby recovering several metals. Precipitation of metals with HSâ» was fast and produced fine precipitates. The pH of acid mine water is about 2â4, and it can be adjusted to pH 5.5 before sulphide precipitation, while the precipitation, on the other hand, requires a sulphide solution with pH at 8 and the sulphide in HSâ» form. This prevents HâS formation and mitigates the risk posed from the evaporation of toxic hydrogen sulphur gas. This is a lower increase than is required for hydroxide precipitation, in which pH is typically raised to approximately nine. After precipitation, metal concentrations ranged from 1 to 30 ÎŒg/L
Sulphate removal from mine water by precipitation as ettringite by newly developed electrochemical aluminium dosing method
Abstract
Precipitation as ettringite (CaâAlâ(SOâ)â(OH)ââ·26HâO) is an effective method for sulphate removal from mine water. The addition of calcium hydroxide and aluminium to sulphate-containing mine water in stoichiometric amounts induces an increase in pH to approximately 12.5, leading to the precipitation of ettringite. Typically, aluminium salts are used as the source of aluminium; however, in this research, an electrochemical dosage of aluminium was used, and the results were compared with the results of chemical ettringite precipitation as well as the results of computational simulations of sulphate removal. The mine water sulphate concentration was reduced 99.0% and 98.6% from the initial 1,060 ± 20 mg Lâ»Âč using a current density of 28 mA cmâ»ÂČ in electrochemical aluminium dosing and chemical aluminium dosing, respectively, which was close to the theoretical 100% sulphate removal. When using the current density of 28 mA cmâ»ÂČ in the electrochemical aluminium dosing, the recovered ettringite purity was 92.5%, which was almost the same as the 92.6% purity in the chemical aluminium dosing characterised with X-ray diffraction and Rietveld analysis. The results indicate that the electrochemical dosing of aluminium could be an alternative to aluminium salt application in ettringite precipitation
Phosphate and ammonium removal from water through electrochemical and chemical precipitation of struvite
Abstract
Batch electrocoagulation (BEC), continuous electrocoagulation (CEC), and chemical precipitation (CP) were compared in struvite (MgNHâPOâ·6HâO) precipitation from synthetic and authentic water. In synthetic water treatment (SWT), struvite yield was in BEC 1.72, CEC 0.61, and CP 1.54 kg/mÂł. Corresponding values in authentic water treatment (AWT) were 2.55, 3.04, and 2.47 kg/mÂł. In SWT, 1 kg struvite costs in BEC, CEC, and CP were 0.55, 0.55, and 0.11 âŹ, respectively, for AWT 0.35, 0.22 and 0.07 âŹ. Phosphate removal in SWT was 93.6, 74.5, and 71.6% in BEC, CEC, and CP, respectively, the corresponding rates in AWT were 89.7, 77.8, and 74.4%. Ammonium removal for SWT in BEC, CEC, and CP were 79.4, 51.5, and 62.5%, respectively, rates in AWT 56.1, 64.1, and 60.9%. Efficiency in CEC and BEC are equal in nutrient recovery in SWT, although energy efficiency was better in CEC. CP is cheaper than BEC and CEC
Removal of zinc from submerged arc furnace flue gas wash water using steel slag with polyacrylamide
Abstract
The aim of this research was to investigate zinc removal from submerged arc furnace flue gas wash water with steel slag and polymer treatment. The current treatment for the submerged arc furnace flue gas wash water is treatment with polymer only which aids in the settling of particulate zinc. However, in this research enhanced removal of zinc by also precipitating soluble zinc using steel slag was studied. The zinc removal results were compared with the results using commercial neutralizing agents NaOH, Mg(OH)â, and Ca(OH)â together with polymer. The precipitation conditions were simulated with MINEQL + software and the calculated results were compared with the results from laboratory jar test experiments. Zinc was removed to less than the target concentration 2 mg/l with steel slag and polymer treatment at pH 9. Additionally, turbidity of the treated water decreased to 20 NTU compared to the initial 860 NTU. However, the amount of steel slag needed in the treatment was significantly higher than the amounts of NaOH and Ca(OH)â. The main zinc removal mechanism of steel slag was precipitation as zinc oxide. Calculated zinc removal was higher than the experimental which indicates that equilibrium was not reached in the precipitation experiments which could be due to relatively short contact time chosen to simulate the actual process conditions at the plant
The use of industrial waste materials for the simultaneous removal of ammonium nitrogen and phosphate from the anaerobic digestion reject water
Abstract
The European Unionâs circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste materials and side flows is required to be more effective. In this research, a chemical precipitation method to simultaneously remove ammonium and phosphate from the reject water of anaerobic digestion plant using calcined paper mill sludge and fly ash as a precipitant, was tested. Paper mill sludge is a waste material formed in the paper-making process, and fly ash is another waste material formed in the power plant. Objective of this research was to test whether these industrial waste streams could be used as low cost precipitation chemicals for ammonium and phosphate removal from wastewaters and whether the precipitate could be suitable for fertilizer use. Results indicated that calcined paper mill sludge had high removal efficiency for both ammonium (97%) and phosphate (73%). Fly ash also had good removal efficiency for both ammonium nitrogen (74%) and phosphate (59%) at 20â±â2 °C. The precipitates contained high concentrations of nitrogen and phosphate and could be used as a recycled fertilizer. Other possible mechanisms for the removal of phosphate and ammonium were considered
Removal of sulphate and arsenic from wastewater using calcium sulfoaluminate (yeâelimite)
Abstract
Chemical precipitation is one of the most widely known methods for treatment of industrial wastewaters with high sulphate content, where sulphate can be precipitated as practically insoluble ettringite (CaâAlâ(SOâ)â(OH)ââ·26HâO). This treatment method is also widely recognised for solidifying hazardous components and toxic elements e.g. arsenic in wastewater. In the ettringite precipitation process, lime and aluminium salts are typically used as starting materials, in stoichiometric amounts to form ettringite from the sulphate-containing water, leading to a pH rise to âŒ11.5 and ettringite precipitation. In the current study, for the first time, yeâelimite mineral (CaâAlâOââSOâ), also known as calcium sulfoaluminate (CSA) in cements, is used in order to investigate its suitability to form ettringite precipitate from sulphate and arsenic containing synthetic wastewater and industrial wastewater solutions. The dissolution of yeâelimite prior to dosing, optimal precipitation pH, and arsenic co-precipitation were studied. The effluent and precipitates were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM-EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-OES). The results showed that high percentage of sulphate removal (98% in the synthetic wastewater and 87% in the industrial wastewater) can be achieved using yeâelimite as the aluminium source in ettringite precipitation. Additionally, up to 95% arsenic removal was achieved in arsenic co-precipitation experiments from the synthetic wastewater. The current developed technology can be used as a novel ecological and cost-effective approach for removal of sulphate and toxic elements from wastewater