Experimental Study on Low-Alkali Beneficiation Process for a High-Germanium，High-Sulfur Lead-Zinc Ore in Yunnan AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY25050001

Chinese Library Classification Number:TD952

Citation Information:

A high-sulfur lead-zinc ore from Yunnan，containing valuable associated germanium，presented significant challenges in conventional beneficiation due to its complex mineralogy. Process mineralogy studies revealed that the ore contained 7.08%Pb，20.26%Zn，27.46%S，50.38 g·t^-1 Ag and 26.00 g·t^-1 Ge，with lead and zinc mainly occurring as galena and sphalerite. Pyrite accounted for about 32% of the mineral composition，and both galena and sphalerite exhibited fine-grained，uneven dissemination：galena was mostly in the range of –2.56+0.04 mm and sphalerite in –10.24+0.16 mm，making liberation and selective flotation difficult. The traditional high-alkali process （using large amounts of lime） commonly applied to such ores suffered from severe mutual contamination between lead and zinc concentrates，high reagent costs，expensive wastewater treatment due to alkaline discharge，and poor recovery of germanium，which was mainly hosted in sphalerite and tended to be lost in tailings under high pH conditions. To overcome these problems，a novel low-alkali preferential flotation process was developed based on the surface property differences of galena，sphalerite and pyrite，without any lime addition. After determining the optimal grinding fineness of 75% passing 0.074 mm，lead flotation was carried out using zinc sulfate as the depressant for sphalerite and a newly developed phosphonate ester collector P1. P1 collector exhibited strong selective affinity for lead atoms on galena surfaces via coordination bonding，while showing negligible interaction with zinc and iron atoms，thus effectively collecting galena without floating sphalerite or pyrite. A closed-circuit lead flotation flowsheet consisting of one rougher，three cleaners and three scavengers yielded a lead concentrate assaying 66.86% Pb with a Pb recovery of 88.88%. The lead concentrate also contained 350.25 g·t^-1 Ag，corresponding to an Ag recovery of 65.59%. The zinc content in the lead concentrate was only 5.00%，significantly lower than that obtained with the conventional high-lime process，demonstrating excellent selectivity. The tailings from the lead circuit were then subjected to zinc flotation. Copper sulfate was added as an activator to replace surface Zn²⁺ with Cu²⁺ on sphalerite，forming a copper sulfide film that enhances collector adsorption. A mixed thionocarbamate collector P2 was introduced as the zinc collector. Under low-alkaline conditions （natural pH~8.5），the zinc flotation circuit comprising one rougher，one cleaner and two scavengers produced a zinc concentrate grading 54.44% Zn with a Zn recovery of 95.11%. The zinc concentrates also contained 28.85 g·t^-1 Ag and 58.08 g·t^-1 Ge，corresponding to Ag recovery of 20.26% and Ge recovery as high as 77.12%. Germanium，which was largely enriched in the zinc concentrate due to its solid-solution occurrence in sphalerite，could thus be further recovered by subsequent hydrometallurgical processes，providing an additional economic benefit. A subsequent sulfur flotation stage using ethyl xanthate recovered a sulfur concentrate with 51.54% S，achieving a S recovery of 38.58% from the lead-zinc tailings. Compared with the original plant process （a typical high-lime flowsheet），the new low-alkali process achieved a 2.88 percentage point increase in Pb recovery （from 86.00% to 88.88%） and a 1.78 percentage point increase in Zn recovery （from 93.33% to 95.11%）. More importantly，the recovery of associated silver in the lead concentrate increased from 51.03% to 65.59%，and the recovery of germanium in the zinc concentrate rose from 65.83% to 77.12%，indicating that the low-alkali environment prevents surface passivation of germanium-bearing minerals and allows efficient activation and collection. The elimination of lime also reduced reagent costs by approximately 10.36 RMB per ton of raw ore，and the tailings wastewater had a near-neutral pH （7.5~8.5），requiring no acid neutralization and substantially lowering wastewater treatment expenses. The mutual contamination between lead and zinc concentrates was markedly reduced，which improved the market value of both products and reduces smelter penalties. The successful development and validation of this low-alkali preferential flotation process，using the novel collectors P1 and P2，demonstrated that high-sulfur lead-zinc ores containing precious and rare metals like germanium could be efficiently separated without lime. The process not only achieved superior metallurgical performance but also offered significant environmental and economic advantages. It provided a practical and sustainable alternative to conventional high-alkaline technologies and served as a valuable reference for the low-alkali beneficiation of similar complex lead-zinc ores.