This paper presents a new environmental approach for reducing environmental impacts of two local Palestinian industries: It implements the principle of ''treating waste by waste.'' The technical feasibility of chromium removal from wastewater in leather making by its treatment with solid waste from stone cutting industry is demonstrated experimentally, and found to be an efficient approach. Nearly full removal of chromium is obtained at optimum operating conditions using sufficient mass of solid waste (limestone) and allowing enough contact time between the two wastes. This study investigated effects of various parameters on the percentage relative decrease in concentration by using ultra violet (UV)/Vis spectrophotometry. Kinetic curves showed that percentage relative decrease in concentration increased with time until approaching a plateau (adsorption capacity). The adsorption capacity increased with increasing limestone to liquid ratio (solid content), until nearly full removal of chromium was obtained when the solid content was 5 g/100 mL or higher. This was accomplished within few days when the particles were settled. The adsorption capacity was pH dependent; adsorption at pH < 5 was obtained, as a finding which was not reported by previous investigators for Cr(III) adsorption using other particles. The percentage removal was nearly doubled at higher pH values (>5). Further research work is proposed to distinguish between the contributions of the two removal mechanisms of precipitation and adsorption.

Leather industry consumes large amounts of chemicals, particularly toxic chromium sulfate. 30-40% of chromium used in this industry is released as a solid or liquid waste, which eventually ends up in soil and ground water. This work aims at determining the total chromium in samples of tannery wastewater and removing it using Cactus as adsorbent. Detection of chromium (VI) and total chromium was performed spectrophotometricaly using 1.5-diphenylcarbazide reagent in addition to diazo-coupling reaction (between sulphanilic acid and N, N-dimethylaniline). The efficiency of removing chromium ions from contaminated tannery wastewater by adsorption on cactus powder was investigated by batch experiments and the effects of various parameters (pH, adsorbent dosage and treatment time) on the percentage removal of chromium were investigated. The percentage removal obtained was 98.8% for chromium (VI) and 97.0% for chromium (III) at optimum conditions: pH = 8, adsorbent dosage equal 6.0 g/l and contact time of 60 min. The results of this work demonstrated for first time that removing chromium ions, especially carcinogenic chromium (VI), using cactus powder is more efficient than commonly used calcium carbonate.