OPERATIONALLY DETERMINED CHEMICAL SPECIATION OF BARIUM AND CHROMIUM IN DRILLING-FLUID WASTES BY SEQUENTIAL EXTRACTION

A study has been conducted to determine the influence of pH on the spe ciation and distribution of barium and chromium in drilling mud. Sampl es in equilibrium under controlled conditions were subjected to sequen tial extraction procedure to fractionate the heavy metals into the des ignated forms of exchangeable, adsorbed, organically bound, carbonate and residual phases. This provides an insight into the potential avail ability of the heavy metals for possible release into groundwaters and /or surface waters. The major portion of both the metals studied was f ound in the carbonate and residual forms with the relative distributio n depending on the pH. Generally, decreasing pH caused a shift from th e residual form towards the carbonate or organic forms of metals. The occurrence of metals in more stable organic, carbonate and residual fo rms in drilling mud, coupled with no significant release to the aqueou s phase upon varying the pH indicates the resistance of these metals t o remobilisation from drilling mud.