Chromium (III) is an inorganic salt being used as corrosion inhibitor plating agents surface treating agents furniture furnishings and textile printing and etc. The discharge of industrial waste water containing chromium (III) into the water source was toxic to the aquatic lives and some parts accumulate in the soil chromium (III) reduces the growth of plants reduced photosynthesis inhibit the enzyme activity imbalanced in plants and reduced productivity and etc. For this reason method to remove it before discharge the effluent into the water source is necessary. The use of apatite materials for adsorption and immobilization of various pollutants was a technique that was more likely to be used.Due to its high adsorbency easy to use and environmentally friendly. The purpose of this research was to study the preparation of calcium hydroxyapatite structural characterization of calcium hydroxyapatite by X-ray diffraction technique adsorption study of chromium solution with calcium hydroxyapatite in various conditions and the determination of adsorption isotherm. The results showed that the optimum contact time of calcium hydroxyapatite and chromium solution was 3 hours. Most adsorption works well at a pH of around 6.76. Considering the amount of chromium (III) adsorbed at equilibrium (q) it was found that the calcium hydroxyapatite with 10 % zinc added that has been calcined to 400 OC and the calcium hydroxyapatite with 15 % zinc added that has been calcined to 800 OC were to adsorb chromium (III) more than other sorbents. The adsorption isotherm was suited with Fruendlich and Langmuir. The calcium hydroxyapatite with 10 % and 15 % zinc added that has been calcined to 400 OC had the highest adsorption capacity (qm) up to 178.57 and 181.82 mg/g respectively. In addition it was found that calcium hydroxyapatite which heated to 800 degrees Celsius can decompose tricalciumphosphate.

This research is aimed at investigating the amount of chromium carbide (Cr23C6) in stainless steel AISI 304 by electrochemical technique testing in calculating the Pa values that corresponding to sensitization stage and the corrosion behavior. The results will carry on to developing the welding process. The specimens were produced with Shielded Metal Arc Welding method. Moreover it was bending at the angle 0 90 and 180 degree and the process finished on post-heat treatment with different cool down conditions are 800ºC annealed in air cooled 1100ºC annealed in water cooled and annealed 1100ºC in air cooled respectively. The results show that: first conditional is appeared the maximum amount of Pa value (Pa > 0.4) indicating that more precipitation of Cr23C6 in heat affected zone (HAZ) of specimen. The second conditional is not found the sensitization stage because when the specimens were annealed at high temperature the chromium carbide will break up and residual stress in HAZ will decrease. At last conditional is found the less amount of Pa value; the reason of using high temperature on annealing process will decrease chromium carbide but slowly air-induced cooling must pass the critical temperature then some Cr23C6 will appear at grain boundary and cause of high corrosion rate. Concerning to the corrosion behavior the second conditional present the lowest corrosion rate corresponding to the better-quality of passive film. Whereas the first conditional shown the highest corrosion rate and low quality of passive film. Thus 1100ºC annealed with water cooled is excellent condition for developing the welding process.