Using ferronickel slag as raw material, adding nitric acid and surfactant to modify its mineral phase, a modified ferronickel slag adsorbent was prepared, and the effects of surfactant type, cetyltrimethylammonium bromide (CTAB) dosage, adsorbent dosage, initial pH value of solution, Cr(VI) concentration on Cr(VI) adsorption were investigated. The results show that amorphous SiO2 with loose structure and high specific surface area of 180.6 m2/g is prepared from ferronickel slag after modification. The adsorption rate of modified ferronickel slag on Cr(VI) reaches 90% within 10 min. The adsorption isotherm conforms to the Langmuir model, the maximum theoretical adsorption capacity is 42.55 mg/g, and the adsorption kinetics conforms to the pseudo-second-order kinetic model. The adsorption mechanism of Cr(VI) by modified ferronickel slag adsorbent is mainly physical adsorption and redox, that is, the Van der Waals force on the surface of adsorbent adsorbs HCrO -4 to the surface of adsorbent, and the electron pair provided by CTAB reduces Cr(VI) to Cr(III). The amorphous SiO2 with high specific surface area obtained by modified ferronickel slag can not only adsorb and purify Cr(VI) effectively, but also realize the resource utilization of ferronickel slag to achieve the purpose of treating pollution with waste, and has good environmental effects and economic benefits.