Efficient chemical stabilization of tannery wastewater pollutants in a single step process: Geopolymerization

Giacomo Boldrini,Luisa Barbieri,Marco Giorgetti,Isabella Lancellotti,Caterina Sgarlata,Michela Ciabocco,Cristina Leonelli,Mario Berrettoni,Silvia Zamponi

doi:10.1186/s42834-021-00106-7

Abstract

The treatment of tannery wastewaters is a complex task due to the complexity of the waste: a mixture of several pollutants, both anionic and cationic as well as organic macromolecules which are very hard to treat for disposal all together. Geopolymers are a class of inorganic binders obtained by alkali activation of aluminosilicate powders at room temperature. Such activation process leads to a cement like matrix that drastically decreases mobility of several components via entrapment. This process taking place in the matrix can be hypothesized to be the in-situ formation of zeolite structures. In this work we use a metakaolin based geopolymer to tackle the problem directly in an actual industrial environment. To obtain a geopolymer, the metakaolin was mixed with 10 wt% of wastewater added with sodium hydroxide and sodium silicate as activating solutions. This process allowed a rapid consolidation at room temperature, the average compressive strength was between 14 and 43 MPa. Leaching tests performed at different aging times confirm a high immobilization efficiency close to 100%. In particular, only the 0.008 and 2.31% of Chromium and Chlorides respectively are released in the leaching test after 7 months of aging.

Highlights

Hazardous waste management involves the reduction of the amount of hazardous substances produced, or treatment of hazardous wastes, to reduce their toxicity, preferably using green technologies
The Scanning Electron Microscopy (SEM) observation coupled with Energy Dispersive X-ray (EDS) analysis shows the homogeneous microstructure where an amount of 0.5 wt% of Cr was detected (Fig. 2a where Back-Scattered Electrons (BSE) image is reported)
4100 mg L−1 no Conclusions A significant number of operations within a tannery industry are wet operations consuming large amounts of liquids leading to large amounts of polluted water requiring special treatment due to the high concentration of Cr (III) ions and the presence of other chemical reagents that are toxic or harmful for the environment

Summary

Introduction

Hazardous waste management involves the reduction of the amount of hazardous substances produced, or treatment of hazardous wastes, to reduce their toxicity, preferably using green technologies. Even though in the past 15 years the Chinese leather industry has grown at a fast pace, Italy still retains its this positive data has a drawback: the tanning industries produce a large amount of liquid waste (for the total process is estimated at 100 L for m2 of leather [3]) that is difficult to treat before disposal with high toxic potential due to chromium, soluble anions and surfactant content.

Methods

Results

Conclusion