This article deals with hydrometallurgical treatment with the subsequent precipitation of zinc from hazardous waste Sal-Ammoniac Skimming produced in wet hot-dip galvanizing process. Chemical analysis showed that skimming contained 46.64% Zn. X-ray diffraction analysis identified the Zn(OH)Cl phase (96.36%) and NH 4 Cl (3.64%) in Sal-Ammoniac Skimming. The skimming was first subjected to leaching in order to extract zinc into the solution containing HCl, followed by precipitation of the zinc. The experiments were performed in a medium of HCl at concentrations of 0.25, 0.5, 1 and 2M. Complete dissolution of zinc was achieved in 0.5M HCl solution, at 40°C, L:S=20, max. 30 min. The apparent activation energy of leaching reaction by hydrochloric acid solution was Ea=5.543 kJ mol -1 . Zn precipitation was carried out using Na 2 CO 3 and NaOH. Zinc oxide with a purity of about 99% was obtained directly from the solution of 6M NaOH at a temperature of 60°C -80°Cat pH 8.8.
ApstraktOvaj rad se bavi hidrometalurškim postupkom sa naknadnim taloženjem cinka iz opasnog otpada, odnosno pene amonijum hlorida nastale tokom postupka toplog cinkovanja u vlažnim uslovima. Hemijska analiza je pokazala da pena sadrži 46,64% cinka. Rentgenskom difrakcijom je ustanovljeno postojanje dve faze u peni amonijum hidroksida, faza Zn(OH)Cl (96.36%) kao i faza NH4Cl (3.64%). Pena je najpre lužena da bi se izdvojio cink u rastvoru HCl, da bi nakon toga došlo do taloženja cinka. Eksperimenti su izvedeni u prisustvu HCl, pri koncentracijama 0,25, 0,5, 1 i 2M. Potpuno razlaganje cinka je postignuto u rastvoru HCl koncentracije 0,5M, na 40°C, u odnosu T:Č=20, u periodu od maksimalno 30 min. Dobijena energija aktivacije reakcije luženja u prisustvu hlorovodonične kiseline iznosila je Ea=5.543 kJ mol-1. Taloženje cinka je postignuto u prisustvu Na2CO3 i NaOH. Cink oksid, čistoće 99%, dobijen je direktno iz rastvora 6M NaOH na temperaturi od 60°C -80°C pri pH vrednosti 8,8.
Hot-dip galvanizing is one of the most widely used method for protecting of structural steels against corrosion. In general galvanizing process dross called as "hard zinc" is formed on the bottom of the zinc bath. It is formed by the reactions between molten zinc and iron particles in the galvanizing kettle. Hard zinc represents valuable secondary raw material because of the high content of metallic zinc (94-97%). Bottom dross, being an alloy of zinc and intermetallic phase crystals containing 3-6% wt. Fe, has no direct use in the galvanizing process. For this reason there are attempts to elaborate the technology of obtaining a refined zinc containing less then 0,05% wt. Fe. Hard zinc refining with aluminium is one of the method for iron removing. Refining process is based on the formation of intermetallic particles of Al x Fe y type. Refining of hard zinc through removal of iron has been investigated in this study. The effect of various aluminium additions as a refining agent has been studied. Light microscopy and AAS (Atomic absorption spectroscopy) have been used in the evaluation of the refining process.
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