The impacts of treated wastewater on Pb-Zn sulfide flotation performance and potential improvement

In practice, most mineral processing plants operate wet, and fully dry flowsheets remain the minority. Thus, water scarcity is a critical challenge in ore beneficiation plants, and replacing fresh water with a secondary source, such as treated municipal wastewater, must be considered. However, the presence of organic matter and microorganisms in such water can affect flotation performance by (i) forming adsorbed organic layers on sulfide surfaces that hinder collector attachment and (ii) biodegrading xanthate collectors, reducing their effective concentration. As an innovative approach, various water resources (deionized, tap, and treated wastewater) were used at bench scale with real ore to explore the actual effects of these waters on zinc and lead flotation responses (metallurgical recovery and kinetics). The mineral surfaces, slurry, and froth phase were considered. To reveal the mechanisms and interactions during the process, UV-Vis and FTIR were used, and image analysis was conducted to quantify the number and size of froth bubbles. Results showed that treated wastewater produced the fewest bubbles and the largest bubbles, indicating reduced froth stability. Flotation tests showed that treated wastewater reduced galena recovery from about 81.19 to about 68.46% and only slightly affected sphalerite recovery. Surface analyses indicated that Sodium Ethyl Xanthate biodegraded more readily than Sodium Isopropyl Xanthate in treated wastewater and that microbial interactions reduced collector adsorption on galena. Process outcomes from mixed-water scenarios show that conditioning and reagent makeup using tap or deionized water, followed by slurry preparation with treated wastewater, can limit these adverse effects and improve lead recovery. • This study uniquely investigates flotation using real Pb-Zn ore under multiple wastewater-mixture conditioning scenarios, unlike prior work based on pure minerals or laboratory-cultivated bacteria. • Treated municipal wastewater reduced galena recovery from 81 to 68% due to microbial degradation of xanthate collectors and adsorption of organic substances on mineral surfaces. • Conditioning reagents in deionized or tap water, while preparing the slurry with treated wastewater, increased lead recovery to ∼74-76%, demonstrating a practical mitigation strategy for industrial plants. • Spectroscopic analyses (UV-Vis and FTIR) confirmed stronger biodegradation of SEX vs. SIPX and showed that microorganisms simultaneously alter reagent chemistry and galena surface properties, while sphalerite mainly remained unaffected.