Enhanced As (V) Removal from Aqueous Solution by Biochar Prepared from Iron-Impregnated Corn Straw

Table 4

Calculation of saturation indices (SI) for precipitation phases using the equilibrium concentrations in solution at the initial As (V) of 40 mg L⁻¹ in the CS-Fe.

Phase	Reaction	log Ksp	SI
FeAsO42H2O	FeAsO42H2O = Fe^3+ + + 2H2O	−20.2	−3.525
AlAsO42H2O	AlAsO42H2O = Al^3+ + + 2H2O	−15.8	−9.275
Ca3(AsO4)24H2O	Ca3(AsO4)24H2O = 3Ca^2+ + + 4H2O	−18.9	−33.105
Ca5(AsO4)3OH	Ca5(AsO4)3OH = 5Ca^2+ + + OH^−	−40.12	−51.179
Ca4(OH)(AsO4)24H2O	Ca4(OH)(AsO4)24H2O = 4Ca^2+ + + OH^− + 4H2O	−27.49	−51.098

Notes. Calculations performed using the Visual MINTEQ speciation model.