DEVELOPMENT OF TECHNOLOGY FOR PROCESSING SULFURIC ACID WASTE AND CONVERTER DUST

ABSTRACT

The article studies and analyzes methods for processing lead-bismuth sludge from a sulfuric acid production shop and fine dust from an electric precipitator at a converter stage. Methods have been determined for separating the insoluble residue from the solution obtained as a result of salt leaching in the processes of settling and filtration. The relationship between the duration of leaching and temperature on the degree of lead dissolution for each stage was established.  The technological parameters of lead carbonization from the resulting lead chloride solution were studied. It was found that the carbonization process will proceed favorably at a pH of 8.8-9 and a temperature of 60-80°C. It was also revealed that noble metals do not dissolve during salt leaching and during the filtration process melt into the cake and will be processed alternatively.

АННОТАЦИЯ

В статье изучены и проанализированы способы переработки свинцово-висмутовых шламов цеха производства серной кислоы и тонкой пыли электрофильтра конвертерного передела. Определены способы отделения нерастворимого остатка от раствора, полученного в результате солевого выщелачивания в процессах отстаивания и фильтрования. Установлена зависимость продолжительность выщелачивании и температуры на степень расворения свинца для каждой стадии. Изучены технологические параметры карбонизации свинца из полученного раствора хлорида свинца. Было выявлено, что процесс карбонизации будут протекать благоприятно при рН 8,8-9 и температуры 60-80^оС. А также выявлено, что благородные металлы при солевой выщелачивании не растворются и в процессе фильтрации стаются в кеке и будут перерабатыватся алтернативно.

Keywords: fine converter dust, lead-bismuth sludge, table salt, dissolution, pulp, solution, insoluble residue, filtration, clarification, sedimentation, carbonization, pH.

Ключевые слова: тонкая конвертерная пыль, свинцово-висмутовый шлам, поваренная соль, растворение, пульпа, раствор, нерастворимый остаток, фильтрация, осветление, отстаивание, карбонизация, рН.

Introduction. Copper industry dusts are multicomponent products characterized by a diverse chemical, granulometric and phase composition, depending on the feedstock, the specifics of the technology, and the design of process and gas cleaning equipment [1]. Fine dust captured by bag or electrostatic precipitators includes primary particles of the charge, sublimation of light volatile components and their oxidation products in various proportions. The degree of transition of microinclusions into the dust-gas phase also depends on various factors [2], in which, compared with the initial mixture, fine dust is significantly enriched in precious metals and rare elements. Today in our republic industrial waste containing lead is generated in large quantities. In particular, at the copper smelter of the Almalyk Mining and Metallurgical Combine, 50 thousand tons of fine converter dust from the copper smelter and more than 15 thousand tons of lead-bismuth sludge were collected. [3, 4].

The development and implementation of effective technologies for processing intermediate products of gas purification of the copper industry is not only a way to reduce the environmental load, but also to increase the economic efficiency of an industrial enterprise [5].

The work is devoted to the study of methods for processing converter dust and waste from sulfuric acid production in order to extract non-ferrous and precious metals from them.

Methods and results. When determining the content of non-ferrous and noble metals in converter dust and bismuth sludge, the use of X-ray spectral and X-ray fluorescence, atomic emission and atomic absorption spectrometry, as well as mass spectrometric analysis methods made it possible to obtain reliable data on the determination of trace amounts of elements and their distribution in the original product. The average chemical composition of the starting materials is presented in Table 1.

Table 1

Average chemical composition of converter dust and lead-bismuth sludge from the copper smelter of Almalyk Chemical Plant JSC

Discussion. For processing using the chemical enrichment method, converter dust from a copper smelter and lead-bismuth sludge are prepared in a ratio of 80:20%. The resulting mixture was leached (washed) in a lime environment to remove metal sulfates. After washing, the pH value of the solution was increased to 5.5-6 and table salt was leached in two stages according to the developed scheme (Fig. 1).

The NaCl concentration was set at 220 g/l at the first stage of leaching, 180 g/l at the second stage.

During the salt leaching process, lead goes into solution as chloride [6]. Lead chloride dissolves and forms a complex salt in the reverse reaction.

PbCl₂ + 2NaCl = Na₂PbCl₄

Figure 1. Technological scheme for processing converter dust and lead-bismuth sludge

The dissolution of lead sulfate proceeds by the same reaction as the initial chlorination by the reverse reaction.

PbSO₄ + 2 NaCl = PbCl + Na₂SO₄

In addition to lead, zinc and silver can be released into the solution, forming chlorides:         ZnSO₄ + 2NaCl → ZnCl₂ + Na₂SO₄

NaCl + AgCl ↔ Na[AgCl₂]

In order to extract lead from converter dust and lead-bismuth sludge, stage II of the salt leaching process was carried out at temperatures of 50, 70, 90 °C with a concentration of 220 and 180 g/l of sodium chloride.

The duration of leaching was set to 2 hours at each stage with a ratio of T:L = 1:4. To remove lead chloride from undissolved components, the solution was decanted, washed and filtered.

At a high salt concentration, a significant part of the silver passes into the solution, so the studies were carried out at a salt concentration not exceeding 220 g/l.

After salt leaching at stage III, the weight of the sediment decreased by 48%. During the leaching process, lead and some silver passed into the solution, as a result of which the copper, zinc, gold and silver in the cake were enriched almost twice. It is advisable to send the resulting cake together with the copper concentrate to reflective smelting, while the technological performance of the smelting will increase due to the release of gold and silver into the copper matte.

As a result of technological and experimental studies, the optimal technological parameters of the leaching process were determined (Fig. 2).

Figure 2. Dependence of the degree of lead dissolution after stage II salt leaching of converter dust and lead-bismuth sludge on the duration of the process and temperature

Accordingly, at a temperature of 90°C, the degree of lead dissolution in the original product was 94%. After decantation and filtration, the lead contained in the solution was carbonized by adding technical soda in an environment with a pH of 8.8-9.

PbCl₂+Na₂CO₃=2PbCO₃+2NaCl

After carbonization, the precipitate is filtered to obtain PbCO₃ and the solution is used as a circulating solution.

Conclusions. Analysis of the results of the experiments allows us to draw the following conclusions:

- an increase in temperature during the leaching process has a positive effect on the degree of lead dissolution;

- during the salt leaching process, precious metals do not go into solution and are separated during the filtration process, and the cake, in which the content of precious metals has almost doubled, is sent for further processing;

- based on scientific research, an optimal scheme for processing converter dust and lead-bismuth sludge has been developed, which allows not only to extract valuable components, but also to eliminate environmental problems.

References:

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