China Nonferrous Metallurgy

The accurate determination of lead in tungsten ores is of great significance for resource evaluation and beneficiation-metallurgy process control. However, the analysis of high-content lead in high-tungsten matrices has long been challenged by the occlusion of Pb^{2 +} during tungstic acid precipitation and serious interferences from coexisting ions such as Fe³⁺ and Al³⁺. Existing standard analytical methods are mainly suitable for samples with low tungsten or low lead contents and cannot meet the demand for rapid and accurate determination of medium-to-high lead ( >5%) in high-tungsten ores. To address this issue, based on the principle of coordination chemistry, a synergistic tungsten-control system using a tartaric acid-sodium citrate dual masking agent was constructed, and a rapid EDTA titration method was established for the determination of lead in high-tungsten ores. Tartaric acid preferentially complexes W(VI) to form soluble [WO₂(C₄H₄O₆)]^2-, effectively inhibiting the formation of tungstic acid precipitate with an inhibition rate greater than 98%. Sodium citrate selectively chelates Fe³⁺/Al³⁺, eliminating the influence of their hydrolysis on the titration endpoint. The optimal synergistic effect is achieved at a 1:1 ratio of the two masking agents. The optimized determination conditions are as follows: tartaric acid to sodium citrate ratio of 1:1 (total concentration 50 g·L^-1), pH range 5.5-6.0, and masking time 90 s. Under these conditions, spiked recovery experiments showed recoveries of 97.8%-100. 2% (average 99.1%) with a relative standard deviation (RSD) not exceeding 2.1%. Tungsten content interference experiments confirmed that when the WO₃ content is ≤ 200 g·L^-1, the recovery remains above 99. 5% with RSD ≤1. 8%; even when WO₃ reaches 300 g·L^-1, the recovery is still 97.8% (RSD 2.1%), markedly superior to the <95% of traditional methods. Interference test results demonstrate that the relative error is far below 2% under single-element interference of Fe³⁺ or Al³⁺, and it remains below 2% under multi-element synergistic interference (coexistence of Fe^{3 +}, Al^{3 +}, and WO₃). For special interfering elements such as Sb³⁺ and Bi³⁺, complete masking can be achieved by adding only 0.2 g of thiourea, with the relative error decreasing from 0.9% to 0.2%. Six replicate determinations of actual high-tungsten ore samples yielded a standard deviation of 0.02%~0.04% and RSD≤1.3%, and the method exhibited good applicability to samples with varying tungsten contents. This method fills the technical gap in current standards for the determination of high-content lead, effectively solves the problem of Pb²⁺ occlusion in H₂WO₄ precipitate in traditional methods, and provides a new technical solution for the rapid and accurate determination of high-content lead in tungsten ores.