New organic compounds detection and potential removal in crude phosphoric acid using waste sludge

ABSTRACT

Some organic compounds in phosphoric acid are a potential mediator of adverse environmental impacts on soil. This work aims to detect and reduce the content of organic compounds in crude phosphoric acid using waste sludge, from water treatment plants, as a low-cost sorbent. Gas chromatography/mass spectrometry (GC/MS) was used to detect the organic species in crude phosphoric acid, while X-ray fluorescence (XRF), X-ray Diffraction (XRD), scanning electron microscope equipped with energy-dispersive X-ray (SEM/EDAX) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to characterise waste sludges. Practically, three sludge samples (S1 from El-Marg, S2 from Al-Obour and S3 from El-Sheikh Zayed stations, respectively) were utilised and different factors including shaking time, sorbent dose and phosphoric acid concentration were studied.

The results of GC/MS revealed that crude phosphoric acid contains bis [tert-butyl(dimethyl)silyl] azelaate, dibutyl phthalate and 2,6-di-tert-butyl-4-methylphenol as the main organic species. Moreover, the clay content and the surface charge of sludge strongly affect the removal efficiency of organic species. Kinetic analysis using Lagergren pseudo-first-order, pseudo-second-order, Morris-Weber and Elovich models displays that the sorption process using waste sludges is a chemisorption process. The sorption capacity of the applied three sorbents was 26.3, 23.3 and 22.8 mg/g for S1, S2 and S3, respectively, which indicates that the three sludge samples exhibit potential sorbents for the clarification of phosphoric acid and sequentially to produce green phosphate fertilisers.

KEYWORDS:

• Waste sludge
• crude phosphoric acid
• organic species
• sorption

Disclosure statement

No potential conflict of interest was reported by the author(s).