Heavy-metal extraction from sewage sludge using phosphorous-based salts: optimization process with Na₂H₂P₂O₇

Abstract

Land application is one of the important disposal alternatives for sewage sludge, but availability of potential toxic metals often restricts its uses. Three phosphorous-based salts (NaHPO, KPO, KHPO) were studied as potential metal extractants. The conclusions of the research were that greater extractive efficiency is achieved through a 30-min process of vertical shaking with disodium diacid pyrophosphate - NaHPO - at a concentration of 0.2 M at pH 2. Alternatively, the optimized process with oscillating shaking equipment would require 60 min. In both cases the average of set of extracted metals is around 50%. A second extraction process with potassium pyrophosphate - KPO at pH 6 achieved the reduction of further total amounts of metal, upper 65% with respect to the initial content. In this way the sludge could be used in land applications, with restrictions on each soil, according to the limit values specified in the future regulations.

Ionic Liquids as Components of Systems for Metal Extraction

“…Ionic liquids have high sensitivity and selectivity towards many types of analytes, which is due to different mechanisms of interaction, including electrostatic, hydrophobic-hydrophilic, dipole-dipole, and π-π interactions, ion exchange, and hydrogen bonding [4][5][6][7]. Therefore, ILs are being used more and more often in solvent extraction processes related to metal recovery [8][9][10][11][12]. ILs serve as selective extractants for heavy, rare earth, alkali, noble, and radioactive metals.…”

Extraction of Silicon-Containing Nanoparticles from an Agricultural Soil for Analysis by Single Particle Sector Field and Time-of-Flight Inductively Coupled Plasma Mass Spectrometry

“…The impact of this ratio on the extraction process is influenced by several parameters, including the nature of the soil, the type of extractant and the target species. For example, Navarro-González et al [ 52 ] found that an increase in the ratio of extractant (mL) to sludge (g) from 3 to 50 significantly decreased the extraction of heavy metals. On the other hand, Hall and Pelchat [ 53 ] reported minimal variation in the amount of C, Hg or Zn leached from soils when the ratio of extractant volume (mL) to soil mass (g) ranged from 10 to 200.…”