<p>Aiming at the problems of high disposal cost and poor sludge stability in the existing lime-ferric salt method, a new method of preparing low-cost iron-based arsenic precipitant from bulk solid waste copper slag to treat arsenic-containing wastewater was proposed. The optimum preparation conditions of arsenic precipitant were as follows: sulfuric acid concentration 270&#xa0;g/L and liquid-solid ratio 4:1&#xa0;mL/g. Under this condition, Fe₂SiO₄ and Fe₃O₄ in copper slag are dissolved in sulfuric acid, releasing a large number of iron ions and forming a silica gel and sulfate complex. The arsenic removal experiment showed that the residual arsenic concentration of the wastewater with an initial arsenic concentration of 3600&#xa0;mg/L was &lt; 0.5&#xa0;mg/L after reaction at pH = 6, Fe/As molar ratio of 2, reaction time of 2&#xa0;h, and a temperature of 30°C. The mechanism analysis reveals that the removal of arsenic is mainly achieved by the synergistic effect of iron arsenate (FeAsO₄) precipitation and iron oxide (Fe(OH)₃, FeOOH) adsorption, and it is stably fixed in the precipitated arsenic slag. This technology uses copper slag instead of commercial iron salt, significantly reducing the cost of raw materials and realizing the resource utilization of solid waste, and it has a significant industrial application prospect.</p>