Sulfate induced heaving in chromite ore processing residue

Extensive heaving has been observed at sites in New Jersey and Maryland, USA, where chromite ore processing residue (COPR) was deposited. The heaving mechanisms were investigated using confined swell tests on COPR samples collected from deposition sites. The swell tests were conducted using a one-dimensional confined swell test apparatus employing wet and dry cycles with the introduction of different permeants such as tap water, sulfate, chromate and carbonate solutions. These swell tests were completed to evaluate the heaving related to hydrogarnets, ettringite, calcium aluminum chromium oxide hydrate (CAC) and calcite formation. The swell test results showed that significant swell (3%) occurred only upon sulfate addition at 2 wt%. The XRPD analyses of the swelled sample indicated a significant increase in ettringite content which demonstrated that the swell development was strongly associated with the increased ettringite content.