Vol.:(0123456789) 1 3 Waste and Biomass Valorization https://doi.org/10.1007/s12649-019-00696-9 ORIGINAL PAPER Acid‑Assisted Recycling of Iron Hydroxide Sludge as a Coagulant for Metalworking Fluid Wastewater Treatment Phimonphan Mooheng 1,2  · Kullapa Soratana 3  · Tanapon Phenrat 1,2,4 Received: 14 November 2018 / Accepted: 29 April 2019 © Springer Nature B.V. 2019 Abstract Coagulation is capable of treating metalworking fuid (MWF) wastewater after MWF oil recovery, as an alternative fuel by dissolved-air fotation, but it yields a substantial amount of oil-contaminated sludge. The oil-contaminated sludge is a resource of coagulant recovery, which reduces the sludge disposal and coagulant cost. This study examined the acid recovery and reusability of iron coagulant for MWF wastewater treatment. Ferric chloride (FeCl 3 ) was used as a coagulant, while hydrochloric acid (HCl) was used in the solubilisation process. Without MWF contamination, the iron hydroxide (Fe(OH) 3 ) to HCl ratio of 3:1 was required to completely dissolve the Fe(OH) 3 sludge within 5 min. The presence of MWF oil on the sludge substantially decreased the acid recovery of Fe(OH) 3 . Even at 30 min, the Fe(OH) 3 to HCl ratio of 3:1 could recover only 87.07% by mass of iron. The use of anionic polymer (polyacrylate) as a coagulant aid for MWF treatment made the acid recovery of iron coagulant less efective. Acid-recovered iron coagulant can be reused for four cycles to treat the MWF wastewater because increasing the cycles of reuse lowers the treatment efciency. The use of HCl waste in this approach reduces both the operational cost and potential global warming efect. Keywords Metalworking fuid (MWF) wastewater · Ferric chloride (FeCl 3 ) · Coagulation · Acid recovery · Sludge management Statement of Novelty Based on circular economy principle, this study viewed oil- contaminated iron hydroxide sludge from metalworking fuid treatment by coagulation as a raw material for iron coagulant recovery which also reduces of land disposal of the sludge. Although the presence of oil and polyelectrolyte as coagu- lant aid substantially declined the iron recovery efciency, the acid-assisted recycling of oil-contaminated sludge was proven to be technically feasible, allowing four rounds of recycling with appropriate treatment efciency. No study on acid solubilization of oil-contaminated sludge was previ- ously reported. This study also revealed that the use of acid waste in the process, instead of using fresh acid, is a key to make this circular economy approach feasible technically, environmentally, and economically. Introduction The metal manufacturing industry utilises metalworking fuid (MWF; or cutting fuid or coolant oil) in the processes of cutting, turning, drilling, boring, grinding, and milling metal workpieces. The fuid not only fushes out metal chips and fnes from tools and workpieces but also acts as a cool- ant and lubricant during the machining processes [1]. The MWF may be in the form of oil-in-water emulsions. The Special Issue: Waste Management & Valorization—ATHENS 2017 Conference. * Tanapon Phenrat pomphenrat@gmail.com 1 Research Unit for Integrated Natural Resources Remediation and Reclamation (IN3R), Department of Civil Engineering, Faculty of Engineering, Naresuan University, Phitsanulok 65000, Thailand 2 Center of Excellence for Sustainability of Health, Environment and Industry (SHEI), Faculty of Engineering, Naresuan University, Phitsanulok 65000, Thailand 3 School of Logistics and Supply Chain, Naresuan University, Phitsanulok, Thailand 4 Research Program of Toxic Substance Management in the Mining Industry, Center of Excellence on Hazardous Substance Management (HSM), Bangkok 10330, Thailand