ABSTRACT
Chrome is an indispensable input in chemical tanning of pelt. For mass transfer reasons, not more than 80% of the chrome feed is absorbed by the leather leaving a balance of over 20% in the effluent. This leads to material loss if disposed untreated. In addition, the attendant possible oxidation of chromium (III) to chromium (VI) (in the presence of manganese (IV) oxide or under alkaline conditions) known for its carcinogenic effect, makes it necessary to remove good part of the chrome from the effluent before its disposal to sewers or surface water. In this work, treatment CHELTECH (Zaria) tannery's 'mixed effluent' with varying amount of MgO (10 - 60 mg/l) at different contacting times (15 - 120 minutes) reduced the concentration of chromium in the effluent from 29.86 to 0.06 mg/l. This is equivalent to 99.8% chromium removal. The 0.06 mg/l minimum chromium concentration value in the treated effluent falls within the recommended limit for discharge into sewers and surface waters. Chromium recovered from the mixed effluent is known to produce hard leather due to the presence of lime in the effluent. Therefore, segregated spent chromium effluent was treated with varying amount of MgO (50 - 900 mg/l) for 30 minutes. This was able to reduce the chromium from 7020 to 982 mg/l, which is equivalent to 86% chromium removal. The effect of varying contacting time (15 - 75 minutes) using 400 mg/l of MgO reduced the amount of chromium in the effluent by 89.3%. Treatment of the segregated spent chromium effluent offers an effective recovery, as 6268.9 mg/l of chromium was removed as against 29.80 mg/l for mixed effluent using the same process.