A method of recovering oil from an oil-bearing formation and treating the resulting produced water which includes dissolved silica, the method comprising: - recovering an oil-water mixture from the oil-bearing formation; - separating oil from the oil-water mixture to produce an oil product and the produced water having the dissolved silica therein; - directing the produced water to a Magnesium Dissolution Reactor containing a mixer; - injecting magnesium oxide in a solid form into the Magnesium Dissolution Reactor; - using the mixer in the Magnesium Dissolution Reactor, mixing the magnesium oxide with the produced water in the Magnesium Dissolution Reactor; - maintaining the pH of the produced water in the Magnesium Dissolution Reactor at 8.5 or less, which includes adjusting the pH of the produced water downwardly by mixing it with an acid upstream of or in the Magnesium Dissolution Reactor; - dissolving magnesium in the Magnesium Dissolution Reactor wherein the Magnesium Dissolution Reactor pre-dissolves the magnesium such that the dissolved magnesium is available to react downstream to efficiently remove silica; - directing the produced water and dissolved magnesium from the Magnesium Dissolution Reactor, indirectly, to a warm lime softener located downstream of the Magnesium Dissolution Reactor; - mixing one or more alkaline reagents with the produced water and raising the pH of the produced water in the warm lime softener to 10.0 to 11.5; - in the warm lime softener, co-precipitating silica with magnesium hydroxide or adsorbing silica onto precipitated magnesium hydroxide; and - directing the produced water and precipitates therein from the warm lime softener to a solids-liquid separator and separating the magnesium hydroxide and precipitated or adsorbed silica from the produced water, wherein there is provided a hydrated lime reactor disposed between the Magnesium Dissolution Reactor and the warm lime softener, and wherein the method includes injecting hydrated lime into the hydrated lime reactor and mixing the hydrated lime with the produced water after the magnesium oxide has been mixed with the produced water and before the produced water enters the warm lime softener. - recovering an oil-water mixture from the oil-bearing formation; - separating oil from the oil-water mixture to produce an oil product and the produced water having the dissolved silica therein; - directing the produced water to a Magnesium Dissolution Reactor containing a mixer; - injecting magnesium oxide in a solid form into the Magnesium Dissolution Reactor; - using the mixer in the Magnesium Dissolution Reactor, mixing the magnesium oxide with the produced water in the Magnesium Dissolution Reactor; - maintaining the pH of the produced water in the Magnesium Dissolution Reactor at 8.5 or less, which includes adjusting the pH of the produced water downwardly by mixing it with an acid upstream of or in the Magnesium Dissolution Reactor; - dissolving magnesium in the Magnesium Dissolution Reactor wherein the Magnesium Dissolution Reactor pre-dissolves the magnesium such that the dissolved magnesium is available to react downstream to efficiently remove silica; - directing the produced water and dissolved magnesium from the Magnesium Dissolution Reactor, indirectly, to a warm lime softener located downstream of the Magnesium Dissolution Reactor; - mixing one or more alkaline reagents with the produced water and raising the pH of the produced water in the warm lime softener to 10.0 to 11.5; - in the warm lime softener, co-precipitating silica with magnesium hydroxide or adsorbing silica onto precipitated magnesium hydroxide; and - directing the produced water and precipitates therein from the warm lime softener to a solids-liquid separator and separating the magnesium hydroxide and precipitated or adsorbed silica from the produced water,