Browsing by Author "Saari, Eija"

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    Improving Nickel Recovery in Froth Flotation by Purifying Concentrators Process Water Using Dissolved Air Flotation
    (MDPI AG, 2023-03) Aaltonen, Annukka; Le, Thi Minh Khanh; Saari, Eija; Dahl, Olli; Musuku, Benjamin; Lang, Aleksandra; Hiidenheimo, Sakari; Dixon, Richard; School common, CHEM; Department of Bioproducts and Biosystems; Clean Technologies; Metso Outotec Oyj; Outotec Research Center; Metso Outotec España SA
    The pressure for saving water by closing the water loops in mineral processing is increasing continuously. The drivers for higher recirculating rates include water scarcity in dry areas, environmental legislation that is becoming stricter in most countries, limitations set for wet tailings management and the increased demands for social licenses to operate. At the same time, to make mineral processing sustainable, the recovery of valuable minerals should be maximized. This leads for a need to close the process water circulation. To see the effect of closed water circulation on metallurgical performance, flotation tests were carried out with nickel concentrate thickener overflow water before and after the process of water purification by dissolved air flotation (DAF). Both total nickel recovery and concentrate grade in laboratory scale flotation tests to the Ni rougher-scavenger concentrate increased after DAF treatment. Chemical and mineralogical characterizations revealed that after DAF treatment, the process water contained fewer metal hydroxides and less fine-grained silicate mineral particles, which is most likely the reason for the improvement in the nickel flotation performance. Based on the feasibility study, improved nickel recovery by DAF treatment of process water can bring economic benefits at a concentrator plant.
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    Influence of Water Quality on Sulphide Ore Oxidation and Speciation of Sulphur Anions during Autogenous Milling
    (MDPI AG, 2023-02-16) Musuku, Benjamin; Kasymova, Diana; Saari, Eija; Dahl, Olli; School common, CHEM; Department of Bioproducts and Biosystems; Clean Technologies; Outotec Oyj
    Earlier studies at the Kevitsa Cu-Ni concentrator plant have indicated that seasonal variations of the properties of the process water affect the oxidation of the surface of the minerals, and further, the pentlandite flotation performance. However, it is not clear whether the differences in flotation performance are solely due to changes in the mineral surface oxidation, and/or also due to surface oxidation-induced changes in the aqueous phase of the pulp. This paper investigates the effects of the mineral surface oxidation of Kevitsa Cu-Ni ore on the properties of the aqueous phase of the slurry. A systematic study was formulated to monitor the surface oxidation related changes in the mill circuit of the Kevitsa concentrator plant. The study was timed to coincide with a seasonally observed drop in the concentrator plant’s flotation performance, which happens during the summer months (June, July, and August). Both physicochemical parameters, as well as sulphur oxyanions in the plant process water, mill discharge, and hydrocyclone overflows were monitored. Also, the bubble size in selected rougher and cleaner cells was monitored. The results show that season-related changes in mineral surface oxidation cause clear differences in the aqueous phase chemistry of the mill circuit. The increased concentration of reduced sulphur species in the mill discharge is an indication of extensive oxidation of the ore during milling. Also, the bubble size of the flotation cells reacts to the observed seasonal change. The findings of the study confirm that the consequences expected, based on the theory of mineral surface oxidation, are observable downstream in the aqueous phase of the milling circuit. Based on these results, it is not yet possible to say whether the poor flotation performance is caused solely by the oxidation of the mineral surface or also by the properties of the aqueous phase of the slurry after milling. However, the results show that the plant needs both to find ways to limit oxidation rates in the summer, and to consider installing a more robust frother, capable of maintaining efficacy during the warm season. The findings of this study may help the plant to develop ways to enable a timely response to changes in the recycled process water quality, to prevent harmful impacts on pentlandite flotation. The former could be achieved by lowering the temperature of the process water and flotation air, whereas the latter could mean using a different frother.
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    Modifying water circulation of minerals processing plants for higher recovery, grade and environmental reasons
    (2020-08-17) Makarov, Artem; Yazdani, Maryam Roza; Saari, Eija; Insinööritieteiden korkeakoulu; Vahala, Riku
    Current thesis aimed to examine the possibilities to modify water circulation system of minerals processing sites that are working in concentration of sulphide ores. Such sites are facing the issues of thiosalts content in both recycling process water and water streams to be discharged into the environment. Recent studies confirmed that high enough concentration of thiosalts are damaging the site production in terms of worsened efficiency in flotation process leading to lower grade and recovery of the final products. Indirect toxicity of thiosalts for receiving water bodies has been also proved in latest studies. Conventional Fenton method for oxidizing thiosalts with liquid solution of hydrogen peroxide is considered to be efficient but yet costly and hard in an operational control. Current research was meant to find alternative solution of more advanced oxidation in a form of sparging the vaporized hydrogen peroxide into the process water containing thiosalts. It was presumed that increased interaction surfaces for oxidation and decreased contact time consequentially would result in more rapid oxidation and less reagent usage. The laboratory experiments have been conducted with the process water sample from the minerals processing site comparing both conventional Fenton and novel method of thiosalts oxidation. Promising results have been achieved for the advanced oxidation method in terms of process water treatment goals, where the removal percentage does not need to be as ideal as the environmental limits. For the removal of thiosalts till the needed natural levels for discharge water streams, the vaporized hydrogen peroxide yet has proved itself not as efficient. Novel method could reach 89% removal of thiosalts but within quite unrealistic retention time, compared to more rapid conventional Fenton, which reached more than 95% removal rates. The achieved results have been utilized in modeling and simulation work in order to get a full overview of the processes including needed chemical amounts for different volumetric flows of process water and impurities concentration as well as sludge production potential. As a final result, various alternatives and methods for modification in water circulation systems with thiosalts challenges have been compared technologically and economically regarding both thiosalts and sulphates removal technologies from process water streams. Those included methods of hydrogen peroxide oxidation, evaporation, adsorption, ettringite precipitation and membrane filtration. Assessment has been carried out from different perspectives of sustainability, feasibility, investments needed and operational costs to be expected during long term operations of the plants. Several ways towards the continuation of the research have been proposed in order to make sure that both plant and environment could achieve the desired benefits from technologies chosen.
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    Oxidative Dissolution of Low-Grade Ni-Cu Ore and Impact on Flotation of Pentlandite
    (MDPI AG, 2022-11-03) Musuku, Benjamin; Saari, Eija; Dahl, Olli; School common, CHEM; Department of Bioproducts and Biosystems; Clean Technologies; Outotec Oyj
    This paper investigated the effect of mineral surface oxidation on the floatability of Kevitsa low-grade Ni-Cu ore. Physicochemical measurements, ethylene diamine tetra acetic acid (EDTA) extraction, and oxygen uptake experiments were carried out with slurry and recycled process water samples obtained from the Kevitsa Cu-Ni sequential concentrator plant. The pH of recycled process water, copper flotation feed, and nickel flotation feed dropped by 0.7, 0.4, and 0.7 points, respectively, from May to July. The oxygen demand increased from recycled process water to the copper flotation feed, then dropped for the nickel flotation feed. The nickel flotation feed Redox potential (ORP) was lowest for July, while EDTA extractable metals increased from May to July. There was a 20% drop in nickel recoveries from May to July. Based on ORP measurements of the nickel flotation feed, good nickel flotation takes place in a moderately oxidizing (75–170 mV) and alkaline (9.2–9.7 pH) environment. Therefore, the ORP/pH of the nickel flotation feed is important to the nickel flotation. The results showed that at the Kevitsa plant, the grinding process is an electrochemically active environment, which, together with the incoming recycled process water quality, defines the degree of mineral surface oxidation for flotation. The increasing corrosiveness of the recycled process water increased mineral surface oxidation and depressed pentlandite flotation. Laboratory flotation experiments confirmed the observed poor plant flotation response when the corrosiveness of recycled process water increased. Total dissolved solids (TDS) was proven to be a reliable online parameter for the corrosiveness of the recycled process water and was inversely proportional to the pentlandite recovery. The findings of this study may help the plant develop ways to enable a timely response to changes in recycled process water quality to prevent harmful impacts on pentlandite flotation.
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    Simulating the Impact of Ore and Water Quality on Flotation Recovery during the Life of a Mine
    (MDPI AG, 2023-09-19) Aaltonen, Annukka; Izart, Caroline; Lyyra, Mikko; Lang, Aleksandra; Saari, Eija; Dahl, Olli; School common, CHEM; Department of Bioproducts and Biosystems; Clean Technologies; Metso Research Center; Metso Oyj
    Blending of different ore types in the concentrator feed contributes significantly to maintaining a high recovery of valuable minerals with required grades in the concentrate. It is feasible to develop an ore-blending scheme over the life of a mine already in the design phase of the plant. In addition to ore characteristics, water quality is known to impact mineral recovery. A blending plan could also be developed for the different water streams of a future concentrator. This paper describes a novel modeling and simulation approach to predict metallurgical response combining ore types and water quality. The model is based on kinetic laboratory flotation test data, and it was tested on a case study. As a result, rougher flotation grade-recovery curves dependent on ore types and water quality are presented over the predicted life of the mine. The simulation results can be exploited in project design to maximize the recovery of valuable minerals and to ensure environmentally sound and profitable mining operations. Overall, the developed modeling tool can be applied widely for minerals processed by using froth flotation and water types available for kinetic laboratory flotation tests.