Abstract: <SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: "Times New Roman"; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">With industrial waste alkali and brine as raw materials,light magnesia was prepared under the conditions of reaction temperature of <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:chmetcnv w:st="on" TCSC="0" NumberType="1" Negative="False" HasSpace="True" SourceValue="50" UnitName="℃">50 <SPAN lang=EN-US style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman""><SPAN lang=EN-US>℃</SPAN></SPAN></st1:chmetcnv>,calcining temperature of <st1:chmetcnv w:st="on" TCSC="0" NumberType="1" Negative="False" HasSpace="True" SourceValue="850" UnitName="℃">850 <SPAN lang=EN-US style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman""><SPAN lang=EN-US>℃</SPAN></SPAN></st1:chmetcnv>,and calcination holding time of 1 h.With the constant total alkalinity,influences of concentration ratio of sodium carbonate to sodium hydroxide on chloride ion washing and on filtration of intermediate products were studied.Its influences on weight loss rate of precursors,MgO purity,apparent density,citric acid activity (CAA),and particle size distribution were also discussed.Research showed that,in the case of constant total alkalinity,when concentration ratio of sodium carbonate to sodium hydroxide was 1.5</SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-font-kerning: 1.0pt; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman"; mso-bidi-font-family: "Times New Roman"; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">∶</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: "Times New Roman"; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">1,filtration of the intermediate products was the best,chloride ions were more easily to be washed and weight loss rate of precursors was the lowest;at the same time,the product of magnesia with a smaller particle size and uniform distribution was obtained,whose MgO purity was more than 98%;moreover,the product had a smaller apparent density and a better activity,and its chlorine mass fraction was less than 0.03%. </SPAN>