minerals Review A Review on the Beneficiation Methods of Borate Minerals Soehoe-Panhyonon Benedict Powoe 1,†, Varney Kromah 1,2,† , Mohammad Jafari 3,† and Saeed Chehreh Chelgani 4,* 1 Department of Geology and Mining Engineering, Faculty of Engineering, University of Liberia, Monrovia 1000, Liberia; [email protected] (S.-P.B.P.); [email protected] (V.K.) 2 School of Environmental Science and Engineering, Tianjin University, Tianjin 300350, China 3 School of Mining Engineering, College of Engineering, University of Tehran, Tehran 16846-13114, Iran; [email protected] 4 Minerals and Metallurgical Engineering, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden * Correspondence: [email protected]; Tel.: +4-67-3073-7927 † These authors contributed equally to the study. Abstract: The modern boron applications have adsorbed the mineral processors’ attention to improve typical boron mineral’s (BM) beneficiation methods. In this regard, dry treatment and pretreatment processes—such as magnetic separation and calcination as environmentally friendly methods, due to their minimal or zero adverse effect on the environment—need more consideration. Over the years, anionic flotation has become the main technique for beneficiation of friable BMs; however, there is a gap in the investigation of cationic flotation separation since BMs’ surface negatively charges in a wide pH range. At present, enriching BMs’ flotation via surface modification is taking center stage, which can also be considered for reprocessing long-forgotten BM tailings. As a comprehensive review, this work is going to provide a synopsis of the processes, techniques, optimum parameters, and conditions—such as size reduction, zeta potential, pH, and reagents—which have been employed in Citation: Powoe, S.-P.B.; Kromah, V.; the processing of BMs. Gaps in our understanding of BM’s flotation are presented in the context of Jafari, M.; Chehreh Chelgani, S. A Review on the Beneficiation Methods addressing the existing processes, considering possibilities and rooms for efficiency improvement. of Borate Minerals. Minerals 2021, 11, Considering these gaps may improve the performance of existing methods for processing fine and 318. https://doi.org/10.3390/ ultrafine BMs, and help in the development of new technologies to improve flotation recoveries. min11030318 Keywords: borax; ulexite; colemanite; flotation; magnetic separation; flocculation; calcination Academic Editor: Lev Filippov Received: 12 February 2021 Accepted: 16 March 2021 1. Introduction Published: 19 March 2021 Over 150 Boron “B” minerals (BM) have been recorded, and the most frequent ones are borax or tyncal (Na2B4O5 (OH)4·10H2O), ulexite (NaCaB5O6 (OH)6·5H2O), colemanite Publisher’s Note: MDPI stays neutral (Ca2B6O115H2O), and kernite (Na2B4O7·4H2O) [1–3]. It was reported that boron com- with regard to jurisdictional claims in pounds are generally produced from brines rich in this element [4,5]. Typically, BMs are published maps and institutional affil- naturally found as hydrated oxides of alkali metals (especially sodium and calcium), which iations. lose crystallization water through the heating [6]. Worldwide, the estimated BM reserves exceed a billion metric tons, against a yearly production of about four million tons. Turkey, where the largest borate reserve globally is found, is followed by Russia, South America, and the United States. These four countries/regions account for an estimated 95% of the Copyright: © 2021 by the authors. world’s Boron reserves (data from Eti Maden AS). Simultaneously, countries such as China, Licensee MDPI, Basel, Switzerland. Italy, and Germany meet only the local demand due to their smaller deposits [7]. This article is an open access article BMs have been used in various applications dating from the eighth century when distributed under the terms and applied in the refining and assaying of gold and silver [8]. They have been used in conditions of the Creative Commons several other applications such as medicines, food preservatives, ceramic glazes, and metal Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ fluxes [9]. The modern applications of BMs and boron derivatives include microbicides, 4.0/). insecticides, wood treatment agents, washing products (e.g., detergents and soaps), special Minerals 2021, 11, 318. https://doi.org/10.3390/min11030318 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x FOR PEER REVIEW 2 of 18 Minerals 2021, 11, 318 2 of 18 cides, wood treatment agents, washing products (e.g., detergents and soaps), special al- loys, fertilizers, fire retardants, fiberglass, and heat resistant glass (e.g., Pyrex) [10–13]. BMs also canalloys, be used fertilizers, in the metallurgical fire retardants, industries fiberglass, [2,14]. and Boron heat compounds resistant glass have (e.g., a con- Pyrex) [10–13]. BMs also can be used in the metallurgical industries [2,14]. Boron compounds have a siderable potential to be used in the energy sector where “B” as a hydrogen carrier in the considerable potential to be used in the energy sector where “B” as a hydrogen carrier form of BH4, has a higher hydrogen storage capacity than other hydrides and compounds; in the form of BH , has a higher hydrogen storage capacity than other hydrides and hence, it can be used as a hydrogen4 carrier. However, it was reported that the glass, ce- compounds; hence, it can be used as a hydrogen carrier. However, it was reported that the ramics, and agricultural sectors consume about 80% of refined borates and boric acid pro- glass, ceramics, and agricultural sectors consume about 80% of refined borates and boric duced in the world (Figure 1) [15]. acid produced in the world (Figure1)[15]. others, cleaning 20% and detergent, 2% glass, 48% ceramic industry, 15% agriculture, 15% Figure 1. General applications of boron. Although significant attention has now been drawn to BMs, their Processing poses se- vere challenges. BMs and their associated gangues are usually salt-type minerals, naturally Figure 1. Generalhydrophilic, applications soluble, of boron. and exhibit similar surface characteristics. For instance, coleman- ite and realgar (its associated valuable mineral) show similar water contact angles [16]. AlthoughUlexite, significant borax, attention and associated has now clay been gangue drawn minerals to BMs, exhibit their negativeProcessing zeta poses potentials at all severe challenges.practical BMs pH and [1,2 ,their11,17 associated]. Moreover, gangues BMs are are relatively usually friable;salt-type thus, minerals, their grinding natu- generates rally hydrophilic,fines, whichsoluble, enhance and exhibit slime similar coating surface and loss characteristics. of a sufficient amountFor instance, of valued cole- minerals to manite and therealgar tailings (its [associated18,19]. Furthermore, valuable mineral) the conventional show similar wet water mechanical contact attrition angles and wash- [16]. Ulexite,ing borax, processes and associated used for pretreatment clay gangue ofminerals BMs for exhibit further negative processing zeta promote potentials slime coating at all practicaland pH are [1,2,11,17]. environmentally Moreover, unfriendly BMs are [6 ,relatively20]. All of friable; these obstacles thus, their limit grinding the efficiencies of generates fines,beneficiation which enhance methods slime employed coating in and the processingloss of a sufficient of BMs. amount of valued minerals to the tailingsTherefore, [18,19]. removing Furthermor ganguee, mineralsthe conventional from BMs wet utilizes mechanical several attrition preprocessing tech- and washingniques processes such used as ultrasonic for pretreatment pretreatment of BMs [21 for], attrition-scrubbing/classificationfurther processing promote slime [22,23], and coating andthermal are environmentally decomposition/decrepitation unfriendly [6,20]. [All24]. of These these pretreatmentobstacles limit techniques the efficien- are followed cies of beneficiationby various methods beneficiation employed methods in the such processing as electrostatic of BMs. and magnetic separations [25], and Therefore,flotation removing [4,23 ,gangue26,27]. Theseminerals processes from BMs exhibit utilizes grave several limitations preprocessing and may tech- lead to loss of niques suchBMs as ultrasonic in the tailings pretreatment and cause [21], various attrition-scrubbing/classification environmental problems. Hence,[22,23], theyand need to be thermal decomposition/decrepitationcontrolled and optimized by[24]. size Thes reduction,e pretreatment surface techniques property modification,are followed by zeta potential various beneficiationand pH regulation, methods andsuch the as applicationelectrostatic of and appropriate magnetic reagent separations types. [25], However, and there are flotation [4,23,26,27].gaps in the These scientific processes literature exhibit concerning grave limitations BMs’ Processing and may as accentuatedlead to loss byof the limited BMs in the publicationstailings and cause before various 2010 on environmental BMs referenced problems. in this work. Hence, Therefore, they need this to be work aims to controlled andaddress optimized these gapsby size by reduction, systematically surface reviewing property multiple modification, beneficiation zeta potential methods for BMs to and pH regulation,present aspectsand the thatapplication can improve of appropriate their processing reagent from types. their However, resources there and are offer efficient