Recovery of Zinc from Treatment of Spent Acid Solutions from the Pickling Stage of Galvanizing Plants

Abstract

Typical methods for the treatment of waste pickling solutions include precipitation by alkaline reagents, most commonly calcium hydroxide. As a result, large volumes of galvanic sludge form, containing iron, calcium, sulphates, and a relatively small quantity of zinc (<20%), making Zn recovery not profitable. In summary, state-of-the-art Zn galvanization processes entail the loss of valuable metals and the irrational and expensive handling of spent pickling solutions (SPSs). The resulting conclusion is that there is room for a significant improvement in the way SPSs are treated, with the double goal of enhancing Zn galvanization methods’ economic viability and achieving a lesser impact on the environment’s processes. The experimental results show that it is possible to use SPS as a coagulant to treat the process wastewaters, kept separated, and added with sodium hydroxide. The results in obtaining precipitates with Zn contents higher than 40%, increasing the added advantage of making Zn recovery profitable. The results show the possibility of using SPS as a coagulant in the process of physical-chemical wastewater treatment and sodium hydroxide to obtain a precipitate with a zinc content of more than 40%.

Composition and Leaching Toxicity of Hydrochloric Acid Pickling Sludge Generated from the Hot-Dip Galvanized Steel Industry

“…Sometimes, in addition to a flocculant, some manufacturers also add polyacrylamide (PAM) coagulant aids to play a synergistic role, making it easier to settle and separate the precipitates. 66 − 69 …”

“… 68 − 71 SHPS samples with a high zinc content are generally taken from metal surface processing plants that perform both pickling and galvanization processes, such as wire rope hot-dip galvanization plants and automotive component galvanization plants. 68 , 69 Of course, some large-scale manufacturers also separate pickling waste liquid from stripping waste liquid to facilitate treatment, so the zinc content of the produced pickling sludge is low. 71 , 72 In addition, in a hot-dip galvanization factory, when hanging steel during pickling, the zinc covering the hanging piece (such as hooks, jigs, cages, or baskets) may be partially dissolved into the pickling solution, which will clearly cause the sludge sample to contain trace amounts of zinc.…”

“…Si and Al in SHPS samples may generally come from a silica-particle flocculant and a polyaluminum chloride (PAC) flocculant that are separately used in HPWL treatment. Sometimes, in addition to a flocculant, some manufacturers also add polyacrylamide (PAM) coagulant aids to play a synergistic role, making it easier to settle and separate the precipitates. − …”

“…The main chemical composition of the waste liquid from a galvanization plant in Jieyang, Guangdong Province, China, is shown in Table . Some small manufacturers mix the washing water and stripping solution from the galvanization process with the HPWL from the pickling process and then treat the mixed waste liquid with the NP method; when this method is utilized, the SHPS produced by NP will have a high zinc content. − SHPS samples with a high zinc content are generally taken from metal surface processing plants that perform both pickling and galvanization processes, such as wire rope hot-dip galvanization plants and automotive component galvanization plants. , Of course, some large-scale manufacturers also separate pickling waste liquid from stripping waste liquid to facilitate treatment, so the zinc content of the produced pickling sludge is low. , In addition, in a hot-dip galvanization factory, when hanging steel during pickling, the zinc covering the hanging piece (such as hooks, jigs, cages, or baskets) may be partially dissolved into the pickling solution, which will clearly cause the sludge sample to contain trace amounts of zinc. , …”

Anion exchange separations to produce a suitable electrolyte for the electrodeposition of pure zinc

“…Preliminary potentiostatic experiments have shown us that even a slight iron concentration in the electrolyte may cause severe co-deposition. Also, the enhancement of the hydrogen evolution reaction in the presence of iron, may increase the local pH at the cathode and precipitation may also occur (Carrillo-Abad et al, 2011;Carrillo-Abad et al, 2012;Zueva et al, 2021;Regel-Rosocka, 2010). Since the contamination of other metals results in negative effects both in terms of purity and efficiency of the electrodeposition process, purification of the solution before electrowinning shall be an answer.…”