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 speciation and distribution of barium and chromium in drilling mud. Samples in equilibrium under controlled conditions were subjected to sequential extraction procedure to fractionate the heavy metals into the designated forms of exchangeable, adsorbed, organically bound, carbonate and residual phases. This provides an insight into the potential availability of the heavy metals for possible release into groundwaters and/or surface waters. The major portion of both the metals studied was found in the carbonate and residual forms with the relative distribution depending on the pH. Generally, decreasing pH caused a shift from the residual form towards the carbonate or organic forms of metals. The occurrence of metals in more stable organic, carbonate and residual forms in drilling mud, coupled with no significant release to the aqueous phase upon varying the pH indicates the resistance of these metals to remobilisation from drilling mud.