Alkaline leaching of iron and steelmaking dust

Steel production generates significant quantities of dust and sludge in blast furnaces (BF),basic oxygen furnaces (BOF), and electric arc furnaces (EAF). These dusts contain toxicelements, such as heavy metals, and are thus classified as harmful waste making the disposalof them expensive. In addition, direct recycling of dust back to steel production is hindered dueto the presence of zinc. In this literature survey the alkaline leaching of zinc from iron and steelmaking dusts isreviewed. The characteristics of EAF, BOF and BF dust and their processing based on causticsoda (NaOH) leaching is described. Also some methods, e.g. pre-treatments, to enhanceleaching are introduced. Dusts from iron and steel production consist mainly of ferrous oxides. In addition, theycontain zinc, lead and cadmium oxides as well as minor amount of many other elements. Thezinc content in EAF dust can run up 30 %, when it is usually lower in BOF and BF dusts, around1-3 % and 1.5 %, respectively. Zinc is present mainly as zinc oxide, ZnO (50-80 %), and rest is aszinc ferrite, ZnFe2O4. The dusts are very fine (usually < 0.01 mm) and have tendency to agglomerate. Metal extraction from the dusts is difficult due to their complex composition and finding asuitable process is complicated as each dust is unique. The advantage of caustic soda leachingis its selectiveness in leaching zinc compared to iron compounds. Thus a relatively clean andiron-free solution is obtained and the complicated iron removal processes is avoided. Somefacilities using NaOH leaching have been constructed for dissolving zinc from the steelmakingdusts, but they have been closed as inefficient and expensive. For the optimal leaching conditions 6-10 M NaOH solution, liquid to solid ratio of around 10,and temperature of 80 – 95 °C has been presented. Zinc recoveries of 80-85 % can be reachedbut part of zinc is not dissolved and recovered. ZnO dissolves easily in caustic soda, butZnFe2O4 is highly stable compound and is the major obstruction in the hydrometallurgicalextraction of zinc. Pressure leaching, and microwave or ultrasound assisted leaching has notimproved significantly zinc recovery. For breaking the zinc ferrite structure, pyrometallurgicalprocesses, such as roasting, can be used prior to leaching. By roasting with caustic soda priorto alkaline leaching zinc ferrites can be decomposed and leaching of zinc could be improved.Teräksen valmistuksessa syntyy huomattavia määriä pölyjä ja liejuja masuunissa (BF),konvertterissa (BOF) sekä valokaariuunissa (EAF). Nämä pölyt sisältävät haitallisia aineita,kuten raskasmetalleja, ja ne on siten luokiteltu haitalliseksi jätteeksi, mikä tekee niidensijoittamisen kaatopaikalle kalliiksi. Lisäksi pölyjen sinkkipitoisuus estää niidenkierrättämisen suoraan takaisin teräksen valmistusprosessiin. Tässä kirjallisuuskatsauksessa on tarkasteltu sinkin emäksistä liuottamista raudan jateräksen valmistuksessa syntyvistä pölyistä. Masuuni-, konvertteri- ja valokaariuunipölyjenominaisuuksia sekä niiden liuottamista natriumhydroksidilla (NaOH) on kuvattu. Myös jotainmenetelmiä sinkin liuotuksen parantamiseksi, kuten erilaisia esikäsittelyjä, on esitelty. Raudan ja teräksen valmistuksen pölyt koostuvat pääosin raudan oksideista. Lisäksi nesisältävät sinkin ja lyijyn oksideja sekä pieniä määriä monia muita ainesosia. EAF pölynsinkkipitoisuus voi olla jopa 30 %, kun se on yleensä alhaisempi BOF ja BF pölyissä, noin 1-3 %ja 1,5 %. Sinkki on pölyissä pääosin oksidina, ZnO (50-80 %), ja ferriittinä, ZnFe2O4. Pölyt ovaterittäin hienojakoisia (yleensä < 0,01 mm) ja ovat taipuvaisia agglomeroitumaan. Metallien erottaminen pölyistä on hankalaa johtuen niiden kompleksisesta koostumuksestaja sopivan prosessin löytäminen on vaikeaa sillä jokainen pöly on omanlaisensa. Emäkselläliuottamisen etu on, että sinkki liukenee selektiivisesti verrattuna raudan yhdisteisiin ja sitensaadaan raudaton ja suhteellisen puhdas liuos, ja vältytään monimutkaiselta prosessilta raudanpoistamiseksi. NaOH liuotukseen perustuvia laitoksia on perustettu ennenkin sinkinpoistamiseen teräksen valmistuksen pölyistä, mutta ne on suljettu tehottomina ja liian kalliina. Optimaalisiksi liuotusolosuhteiksi kirjallisuudesta saadaan väkevyydeltään 6-10 M NaOHliuos, neste-kiinteä suhteeksi n. 10 ja lämpötilaksi 80-95 °C. Sinkin saanti on ollut tällöin 80-85 % mutta osa sinkistä ei ole liuennut ja jäänyt ottamatta talteen. ZnO liukenee helpostinatriumhydroksidilla mutta ZnFe2O4 on erittäin stabiili yhdiste ja tärkein este sinkinerottamisessa pölyistä hydrometallurgisin menetelmin. Paineliuotus sekä mikroaaltojen taiultraäänen käyttö liuotuksen apuna ei ole parantanut merkittävästi sinkin saantia.Pyrometallurgisia prosesseja, kuten pasutusta, voidaan käyttää ennen liuotustasinkkiferriittien hajottamiseen. Ennen emäsliuotusta tehty pasutus natriumhydroksidinkanssa hajottaa sinkkiferriitit ja sinkin liukeneminen saadaan parannettu

Ultimate strength of corroded web-core sandwich beams

The corrosive marine environment is a threat to the ultimate strength of steel sandwich structures. Therefore, ultimate strength experiments were carried out in three-point bending for beams with different corrosion exposure times, i.e. one and two years. Standard laser-welded web-core sandwich beams are studied and different corrosion protection systems considered. The beams experienced general corrosion. The thickness reduction in unprotected plates and laser welds is around the typical 0.1 mm/year. This led to an ultimate strength reduction of 10% and 17% for beams with exposure times of one and two years, respectively. The experimental ultimate strength is in agreement with finite element simulations. The ultimate strength was maintained for the beams protected with coating or closed-cell polyurethane (PU) foam.Peer reviewe

Simulation of electrochemical processes during oxygen evolution on Pb−MnO2\mathrm{Pb-MnO_2} composite electrodes

The geometric properties of $\mathrm{Pb-MnO_2}$ composite electrodes are studied, and a general formula is presented for the length of the triple phase boundary (TPB) on two dimensional (2D) composite electrodes using sphere packing and cutting simulations. The difference in the geometrical properties of 2D (or compact) and 3D (or porous) electrodes is discussed. It is found that the length of the TPB is the only reasonable property of a 2D electrode that follows a 1/r particle radius relationship. Subsequently, sphere packing cuts are used to derive a statistical electrode surface that is the basis for the earlier proposed simulations of different electrochemical mechanisms. It is shown that two of the proposed mechanisms (conductivity and a two-step-two-material kinetic mechanism) can explain the current increase at $\mathrm{Pb-MnO_2}$ anodes compared to standard lead anodes. The results show that although $\mathrm{MnO_2}$ has low conductivity, when combined with Pb as the metal matrix, the behaviour of the composite is not purely ohmic but is also affected by activation overpotentials, increasing the current density close to the TPB. Current density is inversely proportional to the radius of the catalyst particles, matching with earlier experimental results. A hypothetical two-step-two-material mechanism with intermediate $\mathrm{H_2O_2}$ that reacts on both the Pb matrix and $\mathrm{MnO_2}$ catalyst is studied. It was found that assuming quasi-reversible generation of $\mathrm{H_2O_2}$ followed by its chemical decomposition on $\mathrm{MnO_2}$, results are obtained that agree with the experiments. It is further emphasised that both the Pb matrix and $\mathrm{MnO_2}$ catalyst are necessary and their optimum ratio depends on the used current density. Yet, additional experimental evidence is needed to support the postulated mechanism.Comment: 35 pages, 14 figures; Electrochimica acta, postprint as accepted; due to the limitation "The abstract field cannot be longer than 1,920 characters", the abstract appearing here is shortened, original is in the PDF file. doi is first valid when it is published electronicall

Lapsuudessa koetun kiusaamisen vaikutukset mielenterveyteen aikuisen mielenterveyskuntoutujan näkökulmasta

Tämän opinnäytetyön tarkoituksena oli selvittää aikuisten mielenterveyskuntoutujien kokemuksia koulukiusaamisen vaikutuksesta heidän omaan mielenterveyteensä. Opinnäytetyön tavoitteena oli tuottaa kokemuksellista tietoa koulukiusaamisen mahdollisista vaikutuksista mielenterveyteen ja siten lisätä valmiuksia ymmärtää kiusaamiskokemuksen merkityksellisyyttä suhteessa mielenterveysongelmiin. Opinnäytetyössä selvitettiin aikuisten mielenterveyskuntoutujien kokemuksia koulu- ja verkkokiusaamisesta ja kokemuksia niiden vaikutuksesta omaan mielenterveyteen, miten heidän mielestään kiusaamista tulisi ehkäistä ja mitkä tekijät auttoivat heitä selviämään kiusaamiskokemuksesta. Opinnäytetyö toteutettiin kvalitatiivisella tutkimusmenetelmällä, aineisto kerättiin teemahaastatteluilla ja analysoitiin sisällönanalyysillä. Tulosten perusteella keskeisinä syinä kiusaamiselle koettiin erilaisuus, ryhmäpaine ja vallanhalu. Kiusattu saattoi myös kiusata. Kiusaaminen oli henkistä, fyysistä, seksuaalista ja joukosta eristämistä. Kiusaamista tapahtui näkyvästi ja salassa ulkopuolisten huomiolta. Sitä tapahtui koulussa, koulun ulkopuolella ja internetin kautta. Henkinen kiusaaminen koettiin fyysistä pahempana. Kiusaamisen koettiin vaikuttaneen koulunkäyntiin suhtautumiseen, internetin käyttöön ja elämän kulkuun. Kiusaaminen kesti vuosia. Koulun henkilökunta ei saanut kiusaamista loppumaan. Kiusaaminen laski kiusatun arvoa muiden silmissä. Kiusaamisen koettiin heikentäneen itsetuntoa, vaikuttaneen identiteettiin, tuoneen vaikeuksia ihmissuhteisiin, aiheuttaneen ahdistusta ja pelkoa, heikentäneen elämänhalua ja traumatisoivan. Kiusaamiskokemuksen käsittely terapeuttisissa hoitosuhteissa auttoi, mutta apua saatiin myös sosiaalisista kontakteista, itsereflektiosta, lääkkeistä, henkisestä kasvusta ja hengellisyydestä. Kiusaamistilanteiden välttämisestä koettiin myös olleen apua ja negatiivisten tunteiden välttämisestä saatiin väliaikaista apua. Opettajilta toivottiin enemmän aktiivisuutta kiusaamisen ehkäisyssä. Koululta toivottiin ehkäisevien toimenpiteiden edistämistä ja terveydenhuollolta tukipalveluita. Myös oppilaiden suvaitsevaisuutta toivottiin edistettävän. Opinnäytetyöstä esille nousseita jatkotutkimusehdotuksia olivat verkkokiusaamisen esiintyvyyden tarkempi tutkiminen ja yksilölle koulukiusaamisesta koituvien haittojen lyhyen ja pitkän aikavälin yhteiskunnallisten kustannusten tutkiminen.The purpose of this bachelor’s thesis was to investigate how adult persons rehabilitating after childhood school bullying have experienced school bullying influencing their mental health. The objective of this bachelor’s thesis was to produce praxis information of the possible effects of school bullying on mental health and then increase the understanding of the effects of bullying on mental health. This bachelor’s thesis examined adult mental health rehabilitees’ experiences of school and cyber bullying and how it affected their mental health and how they think school bullying can be prevented and what helped them to survive bullying. This bachelor’s thesis was produced by qualitative method the material was collected by interviews and analyzed by content analysis. Based on the results, the essential reasons for bullying were thought to be being different, group pressure and desire for power. A bullied victim could also bully others. The forms of bullying were physical, sexual, psychical and isolating from the group. Bullying happened openly and in secrecy from the attention of outsiders. It happened in school, outside school grounds and in cyber space. Psychical bullying was experienced more harmful than physical bullying. Bullying affected the bullied persons’ attitude towards school, their lifespan and the way they used the internet. Bullying lasted for years. School staff could not stop the bullying. Being bullied was experienced to lower the victim’s dignity in the eyes of others. Having been bullied was experienced to lower self-esteem, affect the sense of one’s own identity and affect relationships harmfully, cause anxiety and fear, weaken zest for life and cause psychical trauma. Processing the bullying experience in therapeutic treatment was thought to help, but help was also received from social relationships, self-reflection, drugs, psychical growth and spirituality. Avoiding situations of bullying was also experienced to help and avoiding the negative emotions helped temporarily. More active prevention of bullying was expected from teachers. More preventing measures were expected from school and more supportive services from health care. Also the pupils’ tolerance was expected to be enhanced. Suggestions for further studies that rose from this bachelor’s thesis were to examine the incidence of cyber bullying and the short and long term expenses to society from harm done to an individual from school bullying

Risk factors for first hospitalization due to meniscal lesions - a population-based cohort study with 30 years of follow-up

Background: Meniscal lesions are among the most common injuries of the knee, yet limited epidemiologic data is available on their risk factors. We investigated the association of lifestyle factors and physical strenuousness of work on knee injuries with a focus on meniscal lesions. Methods: We examined a nationally representative sample of persons aged 30 to 59 years, who participated in a comprehensive health examination (the Mini-Finland Health Survey). Subjects without any injury or osteoarthritis in the knee joint at baseline (n = 4713) were subsequently followed via the National Hospital Discharge Register up to 30 years. Results: During the follow-up, 338 knee injuries were identified of which 224 were meniscal lesions. Obesity and regular leisure time physical exercise were associated with an increased risk of first hospitalization due to meniscal lesions (hazard ratio (HR) 1.62 and 95% confidence interval (CI) 1.06-2.48 and 1.53, 95% CI 1.05-2.23, respectively). The types of sports predicting the highest risk of meniscal lesions were ballgames, gymnastics and jogging. Physical strenuousness of work did not predict meniscal lesion. The hazard of other knee injury was increased among those reporting irregular or regular physical exercise at baseline (HR 1.64, 95% CI 1.03-2.64 and 1.88 CI 1.05-2.36, respectively). Smoking or alcohol intake were not associated with knee injuries. Conclusions: Better safety measures in high-risk sports and weight control would likely improve the prevention of meniscal lesions in populations.Peer reviewe