Magnetic Removal of Phosphate from Wastewater Using Schwertmannite

Abstract

A magnetic filtration has firstly been applied to the phosphate removal from wastewater by using schwertmannite, which is ferric oxyhydroxide sulfate with high capacity of phosphate adsorption. High efficiency of phosphate removal without using magnetic seeding was obtained at magnetic intensities of around 1 Tesla, which means no necessity to use a superconducting magnet. The kinetics data of phosphate adsorption have been found to be fitted well with a pseudo-second-order model and adsorption equilibrium data have been explained by the Langmuir isotherm. The effect of pH on the phosphate adsorption in this process was characterized by zeta potential measurement. It is proposed that ligand exchange is a dominant mechanism responsible for phosphate adsorption on schwertmannite.

Semi-continuous Magnetic Removal of Phosphate Using an Iron Oxide Hydroxide Adsorbent and Regeneration of Its Adsorbent

“…The schwertmannite was produced by homogenous hydrolysis of iron ferric salt (Fe 2 (SO 4 ) 3 · nH 2 O) using urea as a neutralizing agent. 1,9) The schwertmannite powder was chemically activated by using 0.05 M sulfuric acid in pH ϳ1.5 where 5 g of the dried schwertmannite was subjected to 200 cc of the diluted acid and well mixed for 30 min at room temperature. Then the filtered sample was washed with distilled water for 3-5 times to remove free surplus sulfate ions till reaching to the neutral pH and finally dried at the temperature less than 40°C.…”

“…In order to compare the adsorption capacity of the activated schwertmannite with the non-activated schwertmannite, the Langmuir isotherm, which was well fitted with the schwertmannite adsorption data in the pervious work, 1) was applied. The Langmuir isotherm that is derived under the assumption of a monolayer adsorption with a constant adsorption energy and the dimensionless adsorbate amount q e can be obtained from Eqs.…”

“…1) To obtain the main practical parameters relating to the magnetic filtration and evaluate the performance of the filter in this process, semi-continuous experiment as schematically shown in Fig. 1 was carried out for different fluid velocities and magnetic intensities.…”

“…Also, it has been reported that the schwertmannite can successfully remove arsenate and phosphate from aqueous solutions. 1,6) Although most adsorbents made of metal oxide require acidic conditions for phosphate removal, the schwertmannite can effectively adsorb phosphate under neutral pH condition.…”

“…Schwertmannite with the ideal formula of Fe 8 O 8 (OH) 6 SO 4 as a chemical adsorbent can be easily separated from its aqueous medium through a magnetic filter under a relatively low magnetic intensity of around 1 T without magnetic seeding. 1) Furthermore, it is a highly reactive nanoscale crystalline material with high adsorption capacity, 2) high solubility and high metastability 3,4) and can be precipitated from acid sulfate aqueous solution in pH range from 2.3 to 3.6 under oxidizing and SO 4 -rich conditions. Due to the high specific surface area and reactivity, the schwertmannite plays an important role in the adsorption or incorporation of mobilizing elements in surface and ground water systems, such as soils and mine tailings impoundments.…”