{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:44:15Z","timestamp":1760244255733,"version":"build-2065373602"},"reference-count":31,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2022,9,17]],"date-time":"2022-09-17T00:00:00Z","timestamp":1663372800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Bollinghaus Steel, S.A."}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Metals"],"abstract":"<jats:p>Fluorspar is considered a critical raw material for the European Union, due to its industrial uses and lack of sufficient extraction in European countries. It is a source for hydrofluoric acid manufacture, this latter chemical being employed, among other uses, in the pickling of stainless steels. From this latter activity, sludge is generated due to the need for used water treatment. In this article, we report a full characterization of this residue, obtained in an industrial plant in Vieira de Leiria, Portugal. Its chemical and mineralogical characteristics were determined, showing that it is mostly a mixture of calcium fluoride and calcium sulfate with some heavy metals content. Thermal behavior allowed us to determine that the material melts at around 950 \u00b0C. The influence of calcining operation on the residue was determined, especially concerned with the leachability of some elements. Taking into account the results of the characterization of this residue, some considerations are presented about the potential for the valorization of this industrial residue.<\/jats:p>","DOI":"10.3390\/met12091539","type":"journal-article","created":{"date-parts":[[2022,9,19]],"date-time":"2022-09-19T02:06:50Z","timestamp":1663553210000},"page":"1539","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Characterization of Stainless Steel Spent Pickling Sludge and Prospects for Its Valorization"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6674-3988","authenticated-orcid":false,"given":"Fernando","family":"Castro","sequence":"first","affiliation":[{"name":"Metrics Research Centre, University of Minho, Azur\u00e9m, 4800-058 Guimar\u00e3es, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7589-1299","authenticated-orcid":false,"given":"Pedro B.","family":"Tavares","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica-Vila Real, Departamento de Qu\u00edmica, ECVA, Universidade de Tr\u00e1s os Montes e Alto Douro, 5000-801 Vila Real, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3600-1094","authenticated-orcid":false,"given":"Nuno","family":"Cristelo","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica-Vila Real, Departamento de Qu\u00edmica, ECVA, Universidade de Tr\u00e1s os Montes e Alto Douro, 5000-801 Vila Real, Portugal"}]},{"given":"Tiago","family":"Teixeira","sequence":"additional","affiliation":[{"name":"W2V, Lda, Rua das Alminhas, 900, Calvos, 4810-608 Guimar\u00e3es, Portugal"}]},{"given":"Joana F.","family":"Garcia","sequence":"additional","affiliation":[{"name":"Bollinghaus Steel, SA, 2431-909 Vieira de Leiria, Portugal"}]},{"given":"Nuno M. G.","family":"Parreira","sequence":"additional","affiliation":[{"name":"Bollinghaus Steel, SA, 2431-909 Vieira de Leiria, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2022,9,17]]},"reference":[{"key":"ref_1","unstructured":"EU Commission (2011). Tackling the Challenges in Commodity Markets and on Raw Materials, European Commission."},{"key":"ref_2","unstructured":"EU Commission (2020). Study on the EU\u2019s List of Critical Raw Materials (2020) Final Report, European Commission."},{"key":"ref_3","unstructured":"(2022, August 22). Available online: https:\/\/pubs.usgs.gov\/periodicals\/mcs2021\/mcs2021-fluorspar.pdf."},{"key":"ref_4","unstructured":"(2022, August 22). Available online: https:\/\/oec.world\/en\/profile\/hs\/fluorspar-97-calcium-fluoride."},{"key":"ref_5","first-page":"2","article-title":"Pickling and passivating stainless steel, Materials and Applications Series","volume":"4","author":"Crookers","year":"2007","journal-title":"Euro. 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