Acid mine drainage is a serious environmental concern in many regions worldwide, but especially in coal and metal mining regions. These acid drainages are often treated with chemicals to raise the pH of the water and to cause neutralization and precipitation of metals. As neutralization occurs, a looser gelatinous material called "floc" is produced. The effects of neutralizing chemical, pH, sulfate to iron molar ratio, and solids concentration on floc settling properties were determined in synthetic acid mine drainage. Sulfate was the important factor affecting floc physicochemical properties, increasing settling times from 25-125% and decreasing settling rates from 24-63%. Neutralization pH, treatment chemical cation and initial solids concentration were less important. Ability of treatment to meet discharge standards also decreased with increasing sulfate concentration. An understanding of sulfate and other solution property effects on floc properties may lead to increased treatment efficiency and improved stream water quality.